Light emitting devices having closely-spaced broad-spectrum and narrow-spectrum luminescent materials and related methods

ABSTRACT

A semiconductor light emitting device includes an LED and an associated recipient luminophoric medium that includes respective first through fourth luminescent materials that down-convert respective first through fourth portions of the radiation emitted by the LED to radiation having respective first through fourth peak wavelengths. The first peak wavelength is in the green color range and the second through fourth peak wavelengths are in the red color range. The second and third luminescent materials each emit light having a full-width half maximum bandwidth of at least 70 nanometers, while the fourth luminescent material emits light having a full-width half maximum bandwidth of less than 60 nanometers. Embodiments that only include three luminescent materials are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from U.S. Provisional PatentApplication Ser. No. 62/222,382, filed Sep. 23, 2015 and from U.S.Provisional Patent Application Ser. No. 62/181,249, filed Jun. 18, 2015,the entire content of each of which is incorporated herein by reference.

BACKGROUND

The present invention relates to light emitting devices and, moreparticularly, to semiconductor light emitting devices that includerecipient luminophoric mediums and to the luminescent materials that areincluded in such recipient luminophoric mediums.

A wide variety of light emitting devices are known in the art including,for example, incandescent light bulbs, fluorescent lights andsemiconductor light emitting devices such as light emitting diodes(“LEDs”). LEDs generally include a series of semiconductor layers thatmay be epitaxially grown on a substrate such as, for example, asapphire, silicon, silicon carbide, gallium nitride or gallium arsenidesubstrate. One or more semiconductor p-n junctions are formed in theseepitaxial layers. When a sufficient voltage is applied across the p-njunction, electrons in the n-type semiconductor layers and holes in thep-type semiconductor layers flow toward the p-n junction. As theelectrons and holes flow toward each other, some of the electrons will“collide” with corresponding holes and recombine. Each time this occurs,a photon of light is emitted, which is how LEDs generate light. Thewavelength distribution of the light generated by an LED generallydepends on the semiconductor materials used and the structure of thethin epitaxial layers that make up the “active region” of the device(i.e., the area where the electrons and holes recombine).

Most LEDs are nearly monochromatic light sources that appear to emitlight having a single color. Thus, the spectral power distribution ofthe light emitted by most LEDs is tightly centered about a “peak”wavelength, which is the wavelength where the spectral powerdistribution or “emission spectrum” of the LED reaches its maximum asdetected by a photo-detector. The “width” of the spectral powerdistribution of most LEDs is between about 10 nm and 30 nm, where thewidth is measured at half the maximum illumination on each side of theemission spectrum (this width is referred to as thefull-width-half-maximum or “FWHM” width).

In order to use LEDs to generate white light, LED-based light emittingdevices have been provided that include several LEDs that each emit alight of a different color. The different colored light emitted by theLEDs combine to produce a desired intensity and/or color of white light.For example, by simultaneously energizing red, green and blue LEDs, theresulting combined light may appear white, or nearly white, dependingon, for example, the relative intensities, peak wavelengths and spectralpower distributions of the source red, green and blue LEDs.

White light may also be produced by surrounding a single LED with one ormore luminescent materials such as phosphors that convert some of thelight emitted by the LED to light of one or more other colors. Thecombination of the light emitted by the single-color LED that is notconverted by the luminescent material(s) and the light of other colorsthat are emitted by the luminescent material(s) may produce a white ornear-white light.

As one example, a white LED lamp may be formed by coating a galliumnitride-based blue LED (i.e., an LED that emits light having a peakwavelength in the blue color range as defined herein) with a yellowluminescent material such as a cerium-doped yttrium aluminum garnetphosphor, which has the chemical formula Y₃Al₅O₁₂:Ce, and is commonlyreferred to as YAG:Ce. The blue LED emits light having an emission witha peak wavelength of, for example, about 460 nm. Some of blue lightemitted by the LED passes between and/or through the YAG:Ce phosphorparticles without being down-converted, while other of the blue lightemitted by the LED is absorbed by the YAG:Ce phosphor, which becomesexcited and emits yellow fluorescence with a peak wavelength of about550 nm (i.e., the blue light is down-converted to yellow light). Thecombination of blue light and yellow light that is emitted by the coatedLED may appear white to an observer. Such light is typically perceivedas being cool white in color, as it is primarily comprises light on thelower half (shorter wavelength side) of the visible emission spectrum.To make the emitted white light appear more “warm” and/or exhibit bettercolor rendering properties, red-light emitting luminescent materialssuch as Eu²⁺ doped CaAlSiN₃ based phosphor particles may be added to thecoating applied to the blue LED.

In general, luminescent materials may absorb light having firstwavelengths and re-emit light having second wavelengths that aredifferent from the first wavelengths. For example, “down-conversion”luminescent materials may absorb light having shorter wavelengths andre-emit light having longer wavelengths. Phosphors are the luminescentmaterials that are most widely used to convert a single-color (typicallyblue or violet) LED into a white light emitting device. However, it willbe appreciated that other luminescent materials may be used that absorblight at one wavelength and re-emit light at a different wavelength inthe visible spectrum such as nanophosphors, quantum dots, scintillators,day glow tapes, and inks that glow in the visible spectrum uponillumination with (e.g., ultraviolet) light.

A medium that includes one or more luminescent materials that ispositioned to receive light that is emitted by an LED or othersemiconductor light emitting device is referred to herein as a“recipient luminophoric medium.” Exemplary recipient luminophoricmediums include layers having luminescent materials that are coated orsprayed directly onto a semiconductor light emitting device or onsurfaces of the packaging thereof, and clear encapsulants (e.g.,epoxy-based or silicone-based curable resin) that include luminescentmaterials that are arranged to partially or fully cover a semiconductorlight emitting device. A recipient luminophoric medium may include onemedium layer or the like in which one or more luminescent materials aremixed, multiple stacked layers or mediums, each of which may include oneor more of the same or different luminescent materials, and/or multiplespaced apart layers or mediums, each of which may include the same ordifferent luminescent materials.

SUMMARY

Pursuant to some embodiments of the present invention, semiconductorlight emitting devices are provided that emit light in at least a bluecolor range, a green color range, a yellow color range and a red colorrange. These semiconductor light emitting devices include an LED and arecipient luminophoric medium that is configured to down-convert atleast some of the light emitted by the LED. The recipient luminophoricmedium includes at least (1) a first luminescent material thatdown-converts a first portion of the radiation emitted by the LED toradiation having a first peak wavelength that is in the green colorrange, (2) a second luminescent material that down-converts a secondportion of the radiation emitted by the LED to radiation having a secondpeak wavelength that is in the red color range, the second luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers, (3) a third luminescent material that down-converts a thirdportion of the radiation emitted by the LED to radiation having a thirdpeak wavelength that is in the red color range, the third luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers, and (4) a fourth luminescent material that down-converts afourth portion of the radiation emitted by the LED to radiation having afourth peak wavelength that is in the red color range, the fourthluminescent material having a full-width half maximum bandwidth of lessthan 60 nanometers.

In some embodiments, the fourth peak wavelength may be greater than thesecond peak wavelength and less than the third peak wavelength. Thesecond peak wavelength may be within 40 nanometers, or within 30nanometers, of the third peak wavelength.

In some embodiments, the combined spectral output of the second andthird luminescent materials in response to the respective second andthird portions of the radiation emitted by the LED may have a peakwavelength in the red color range that is within 20 nanometers of thefourth peak wavelength. The first luminescent material may have afull-width half maximum bandwidth of at least 70 nanometers.

In some embodiments, the fourth luminescent material may emit light inresponse to the fourth portion of the radiation emitted by the LED thathas multiple distinct peaks in the red color range. In such embodiments,a first of the multiple distinct peaks may be at a wavelength that isless than a peak wavelength of a combined spectral output of the secondand third luminescent materials in response to the respective second andthird portions of the radiation emitted by the LED, and a second of themultiple distinct peaks may be at a wavelength that is greater than apeak wavelength of the combined spectral output of the second and thirdluminescent materials in response to the respective second and thirdportions of the radiation emitted by the LED. The first and second ofthe multiple distinct peaks may be the peaks having the highest spectraloutput.

In some embodiments, the first peak wavelength may be between 530 and540 nanometers, the second peak wavelength may be between 620 and 640nanometers and the third peak wavelength may be between 640 and 660nanometers, and the fourth peak wavelength may be greater than thesecond peak wavelength and at least 10 nanometers less than the thirdpeak wavelength. For example, the fourth peak wavelength may be between630 and 640 nanometers.

In some embodiments, the first luminescent material may be a LuAG:Cephosphor, the second luminescent material may be a(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and the third luminescent materialmay be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a higher calciumconcentration than the second luminescent material. The fourthluminescent material may be an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkalimetal and M is an element with a 4+ valence such as, for example, aK₂SiF₆:Mn⁴⁺ phosphor.

A ratio of the first luminescent material to the second, third andfourth luminescent materials by weight may be between 2:1 and 3:1, andwherein a ratio of the second and third luminescent materials to thefourth luminescent material by weight may be between 1:3 and 1:6. Aratio of the second luminescent material to the third luminescentmaterial by weight may be between 3:1 and 1:1.

Pursuant to further embodiments of the present invention, semiconductorlight emitting devices are provided that emit light in at least a bluecolor range, a green color range, a yellow color range and a red colorrange. These semiconductor light emitting devices include an LED and arecipient luminophoric medium that is configured to down-convert atleast some of the light emitted by the LED. The recipient luminophoricmedium includes at least (1) a first luminescent material thatdown-converts a first portion of the radiation emitted by the LED toradiation having a first peak wavelength that is in the green colorrange or the yellow color range, (2) a second luminescent material thatdown-converts a second portion of the radiation emitted by the LED toradiation having a second peak wavelength that is in the red colorrange, (3) a third luminescent material that down-converts a thirdportion of the radiation emitted by the LED to radiation having a thirdpeak wavelength that is in the red color range, and (4) a fourthluminescent material that down-converts a fourth portion of theradiation emitted by the LED to radiation having a fourth peakwavelength that is in the red color range. The fourth peak wavelength isgreater than the second peak wavelength and less than the third peakwavelength, and an emission spectrum of the semiconductor light emittingdevice includes a first peak at the fourth peak wavelength that is atleast 50% greater than any point in the emission spectrum in the yellowor green color ranges.

In some embodiments, the fourth luminescent material may emit light inresponse to the fourth portion of the radiation emitted by the LED thathas multiple distinct peaks in the red color range. The second and thirdluminescent materials may each be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphorthat has a full-width half maximum bandwidth of at least 70 nanometers,and the fourth luminescent material may be a K₂SiF₆:Mn⁴⁺ phosphor thathas a full-width half maximum bandwidth that is less than 60 nanometers.The second peak wavelength may be within 30 nanometers of the third peakwavelength.

Pursuant to still further embodiments of the present invention,semiconductor light emitting devices are provided that emit light in atleast a blue color range, a green color range, a yellow color range anda red color range. These semiconductor light emitting devices include anLED and a recipient luminophoric medium that is configured todown-convert at least some of the light emitted by the LED. Therecipient luminophoric medium includes at least (1) a first luminescentmaterial that down-converts a first portion of the radiation emitted bythe LED to radiation having a first peak wavelength that is in the greencolor range, (2) a second broad-spectrum luminescent material thatdown-converts a second portion of the radiation emitted by the LED toradiation having a second peak wavelength that is in the red colorrange, (3) and a third K₂SiF₆:Mn⁴⁺ phosphor that down-converts a thirdportion of the radiation emitted by the LED to radiation having a thirdpeak wavelength that is in the red color range. The second peakwavelength is within twenty (20) nanometers of the third peakwavelength.

In some embodiments, the spectral output of the semiconductor lightemitting device at the third peak wavelength may be at least 1.5 timesthe spectral output of the semiconductor light emitting device at thesecond peak wavelength. The third peak wavelength may be greater thanthe second peak wavelength. The K₂SiF₆:Mn⁴⁺ phosphor may have multipledistinct peaks, and the two of the multiple distinct peaks having thehighest spectral output have peak wavelengths may be on either side ofthe second peak wavelength.

Pursuant to still further embodiments of the present invention, methodsof manufacturing a semiconductor light emitting device are provided inwhich a narrow-spectrum phosphor is synthesized by (1) dissolving MO₂powder in a first hydrofluoric acid (HF) solution to provide an MO₂+HFsolution, where M is one or more of Si, Ge, Sn, Ti, Zr or Hf, (2) addingdissolved A₂MnF₆ to the MO₂+HF solution to provide a A₂MnF₆+MO₂+HFsolution, where A is an Alkali metal, (3) dissolving AHF₂ in a secondhydrofluoric acid solution to provide an AHF₂+HF solution, (4) addingthe AHF₂+HF solution to the A₂MnF₆+MO₂+HF solution, and (5) extractingsolid precipitates of A₂MF₆:Mn⁴⁺ from the combination of the AHF₂+HF andthe A₂MnF₆+MO₂+HF solutions. A semiconductor light emitting device isprovided that includes an LED and a recipient luminophoric medium thatis configured to down-convert at least some of the light emitted by theLED. The recipient luminophoric medium includes (1) a first luminescentmaterial that down-converts a first portion of the radiation emitted bythe LED to radiation having a first peak wavelength in the green colorrange, (2) a second luminescent material that down-converts a secondportion of the radiation emitted by the LED to radiation having a secondpeak wavelength in the red color range, the second luminescent materialhaving a full-width half maximum bandwidth of at least 70 nanometers,(3) a third luminescent material that down-converts a third portion ofthe radiation emitted by the LED to radiation having a third peakwavelength in the red color range, and (4) a fourth luminescent materialthat includes the A₂MF₆:Mn⁴⁺ precipitates, the fourth luminescentmaterial configured to down-convert a fourth portion of the radiationemitted by the LED to radiation having a fourth peak wavelength in thered color range.

Pursuant to still further embodiments of the present invention,semiconductor light emitting devices are provided that include an LEDand a recipient luminophoric medium that is configured to down-convertat least some of the light emitted by the LED. The recipientluminophoric medium includes at least a first luminescent material thatdown-converts a first portion of the radiation emitted by the LED toradiation having a first peak wavelength that is in the green or yellowcolor ranges, a second luminescent material that down-converts a secondportion of the radiation emitted by the LED to radiation having a secondpeak wavelength that is in the red color range, the second luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers, and a third luminescent material that down-converts a thirdportion of the radiation emitted by the LED to radiation having a thirdpeak wavelength that is in the red color range and that is higher thanthe second peak wavelength, the third luminescent material having anemission peak that has a full-width half maximum bandwidth of less than25 nanometers. In these light emitting devices, the second peakwavelength is within twenty (20) nanometers of the third peakwavelength.

In some embodiments, the third luminescent material may be a K₂SiF₆:Mn⁴⁺phosphor having a peak wavelength between 630 and 640 nm, and the secondluminescent material may be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphorhaving a peak wavelength between 610 and 630 nm. An emission spectrum ofthe semiconductor light emitting device may include a first peak that isattributable to the third luminescent material that is at least 50%greater than any point in the emission spectrum in the yellow or greencolor ranges. The third luminescent material may emit light havingmultiple distinct peaks in the red color range, where a first of themultiple distinct peaks may be at a wavelength that is less than asecond peak wavelength and a second of the multiple distinct peaks maybe at a wavelength that is greater than the second peak wavelength. Insome embodiments, the first and second of the multiple of the distinctpeaks may be the highest two of the multiple of the distinct peaks.

In some embodiments, the first luminescent material may be a YAG:Cephosphor, the second luminescent material may be a(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and the third luminescent materialmay be an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkali metal and M is anelement with a 4+ valence. A ratio of the third luminescent material tothe combination of the first and second luminescent materials by weightmay be at least 2:3. The light output by the semiconductor lightemitting device may have a correlated color temperature of between 2700K and 2850 K, a CRI value of between 80 and 92, a CRI R9 value ofbetween 30 and 70, and a Qg value of between 90 and 110. Thesemiconductor device may be part of a bulb or fixture that does notinclude any red light emitting semiconductor light emitting devices. Thethird luminescent material may emit light having multiple distinct peaksin the red color range, and a peak wavelength of a spectral output ofthe second luminescent material in response to the second portion of theradiation emitted by the LED may be at a wavelength that is within thehighest or second highest of the multiple distinct peaks.

Pursuant to yet additional embodiments, semiconductor light emittingdevices are provided that include an LED that emits light having a peakwavelength in a blue color range and an associated recipientluminophoric medium that is configured to down-convert at least some ofthe light emitted by the LED. The recipient luminophoric medium mayinclude at least a YAG:Ce phosphor, a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor that down-converts a second portion of the radiation emitted bythe LED to radiation having a second peak wavelength that is between 610and 635 nm and an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkali metal and Mis an element with a 4+ valence that down-converts a third portion ofthe radiation emitted by the LED to radiation having a third peakwavelength that is between 625 and 640 nm, the third luminescentmaterial having a full-width half maximum bandwidth of between 25 and 55nm. The second peak wavelength is within twenty (20) nanometers of thethird peak wavelength and the semiconductor light emitting device emitslight having a CRI value of between 80 and 92, a CRI R9 value of between30 and 70, a correlated color temperature of between 2700 K and 2850 K,and a Qg value of between 90 and 110.

In some embodiments an emission spectrum of the semiconductor lightemitting device may include a first peak that is attributable to theA₂MF₆:Mn⁴⁺ phosphor that has a magnitude that is at least twice themagnitude of any point in emission spectrum in the yellow or green colorranges. The A₂MF₆:Mn⁴⁺ phosphor may be at least 70% of the total weightof the combination of the YAG:Ce, A₂MF₆:Mn⁴⁺ and(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors. The A₂MF₆:Mn⁴⁺ phosphor may emitlight having multiple distinct peaks in the red color range, and ahighest of the multiple distinct peaks may be at a wavelength that isgreater than a peak wavelength of a spectral output of the and(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and a second highest of themultiple distinct peaks may be at a wavelength that is less than thepeak wavelength of the spectral output of the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. The A₂MF₆:Mn⁴⁺ phosphor may emitlight having multiple distinct peaks in the red color range, and a peakwavelength of a spectral output of the (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor in response to the second portion of the radiation emitted bythe LED may be at a wavelength that is within the highest or secondhighest of the multiple distinct peaks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a 1931 CIE Chromaticity Diagram illustrating thelocation of the planckian locus.

FIG. 2 is a graph illustrating the response of the human eye to light inthe visible light spectrum.

FIG. 3 is a graph illustrating the intensity of the radiation emitted asa function of wavelength for a conventional state-of-the-artsemiconductor light emitting device that emits warm white light.

FIG. 4 is a schematic cross-sectional view of a semiconductor lightemitting device according to certain embodiments of the presentinvention.

FIG. 5 is a graph illustrating the intensity of the radiation emitted asa function of wavelength for a semiconductor light emitting deviceaccording to certain embodiments of the present invention, and alsoincludes the emission spectra for the conventional semiconductor lightemitting device of FIG. 3 for comparison purposes.

FIGS. 6A-6D are graphs that compare the performance of the semiconductorlight emitting devices used to generate the graphs of FIGS. 3 and 5 interms of luminous flux, color rendering index (“CRI”) performance, CRIR9 performance and color point.

FIG. 7 is a graph illustrating the excitation and emission spectra of anarrow-spectrum red phosphor that may be included in semiconductor lightemitting devices according to embodiments of the present invention.

FIGS. 8A-8D are schematic diagrams illustrating various semiconductorlight emitting devices according to embodiments of the presentinvention.

FIG. 9 is a cross-sectional view of a semiconductor light emittingdevice according to further embodiments of the present invention.

FIG. 10 is a perspective view of a semiconductor light emitting deviceaccording to embodiments of the present invention.

FIG. 11 is a schematic diagram that illustrates a method of synthesizinga narrow-spectrum red phosphor according to embodiments of the presentinvention.

FIG. 12 is a schematic diagram that illustrates additional processingsteps that may be performed to improve the stability of anarrow-spectrum red phosphor formed according to the method of FIG. 11.

FIG. 13 is a flow chart illustrating a method of providing asemiconductor light emitting device according to further embodiments ofthe present invention.

FIG. 14 is a graph illustrating the emission spectra of a semiconductorlight emitting device according to further embodiments of the presentinvention as compared to the emission spectrum for a conventionalsemiconductor light emitting device.

FIG. 15 is a graph illustrating the reflectance spectra for the CRIR1-R9 color samples when illuminated by a reference light source.

FIGS. 16A and 16B are schematic diagrams illustrating semiconductorlight emitting devices according to further embodiments of the presentinvention.

FIGS. 17A-17D are graphs that illustrate the emission spectra and colorquality of a semiconductor light emitting device according toembodiments of the present invention (FIG. 17A) as compared to variousother light emitting devices (FIGS. 17B-17D).

FIG. 18 is a plot of the emission spectra of FIGS. 17B and 17D, alongwith the eye response curve that illustrates the sensitivity of thehuman eye to light of various wavelengths and the CRI R9 reflectivityspectrum.

FIG. 19 is a graph of the emission spectra for a semiconductor lightemitting device according to embodiments of the present invention ascompared to a device that only includes a yellow phosphor and anarrowband red phosphor.

FIG. 20A is a schematic cross-sectional view of a light bulb thatincludes semiconductor light emitting devices according to embodimentsof the present invention.

FIG. 20B is a schematic plan view of a mounting substrate included inthe light bulb of FIG. 20A.

FIGS. 21A and 21B are graphs illustrating the tradeoff between colorquality and luminous flux in conventional devices as well as insemiconductor light emitting devices according to embodiments of thepresent invention.

DETAILED DESCRIPTION

The present invention is directed to semiconductor light emittingdevices having recipient luminophoric mediums that include multiple redlight emitting luminescent materials including at least onenarrow-spectrum red light emitting luminescent material, and to relatedluminescent materials and methods of manufacturing such luminescentmaterials. The semiconductor light emitting devices according toembodiments of the present invention may emit white light and mayexhibit very high luminous flux levels while providing excellent colorrendering performance.

As used herein, the term “semiconductor light emitting device” refers toa light emitting device that includes at least one LED. Thesemiconductor light emitting devices according to embodiments of thepresent invention may be provided, for example, as packaged lamps or asbulbs or light fixtures.

Semiconductor light emitting devices according to embodiments of theinvention may include III-V nitride (e.g., gallium nitride) based LEDsfabricated on a silicon carbide, sapphire or gallium nitride substratessuch as various devices manufactured and/or sold by Cree, Inc. ofDurham, N.C. Such LEDs may (or may not) be configured to operate suchthat light emission occurs through the growth substrate (or asemiconductor layer that was near the growth substrate if the growthsubstrate is removed) in a so-called “flip chip” orientation.Semiconductor light emitting devices according to embodiments of thepresent invention include both vertical devices with a cathode contacton one side of the LED, and an anode contact on an opposite side of theLED and devices in which both contacts are on the same side of thedevice. The design and fabrication of semiconductor light emittingdevices are well known to those skilled in the art, and hence furtherdescription thereof will be omitted.

Visible light may include light having many different wavelengths. Theapparent color of visible light can be illustrated with reference to atwo-dimensional chromaticity diagram, such as the 1931 CIE ChromaticityDiagram illustrated in FIG. 1. Chromaticity diagrams provide a usefulreference for defining colors as weighted sums of colors.

As shown in FIG. 1, colors on a 1931 CIE Chromaticity Diagram aredefined by x and y chromaticity coordinates that fall within a generallyU-shaped area. Colors on or near the outside of the area are saturatedcolors composed of light having a single wavelength, or a very smallwavelength distribution. Colors on the interior of the area areunsaturated colors that are composed of a mixture of differentwavelengths. White light, which can be a mixture of many differentwavelengths, is generally found near the middle of the diagram, in theregion labeled 10 in FIG. 1. There are many different hues of light thatmay be considered “white,” as evidenced by the size of the region 10.For example, some “white” light, such as light generated by sodium vaporlighting devices, may appear yellowish in color, while other “white”light, such as light generated by some fluorescent lighting devices, mayappear more bluish in color.

A binary combination of light from light sources emitting light of firstand second colors may appear to have a different color than either ofthe two constituent colors. The color of the combined light may dependon the wavelengths and relative intensities of the two light sources.For example, light emitted by a combination of a blue source and a redsource may appear purple or magenta to an observer. Similarly, lightemitted by a combination of a blue source and a yellow source may appearwhite to an observer.

Each point in the graph of FIG. 1 is referred to as the “color point” ofa light source that emits a light having that color. As shown in FIG. 1a locus of color points that is referred to as the “black-body” locus 15exists which corresponds to the location of color points of lightemitted by a black-body radiator that is heated to various temperatures.The black-body locus 15 is also referred to as the “planckian” locusbecause the chromaticity coordinates (i.e., color points) that lie alongthe black-body locus obey Planck's equation: E(λ)=Aλ⁻⁵/(e^(B/T)−1),where E is the emission intensity, λ is the emission wavelength, T isthe color temperature of the black-body and A and B are constants. Colorcoordinates that lie on or near the black-body locus 15 yield pleasingwhite light to a human observer.

As a heated object becomes incandescent, it first glows reddish, thenyellowish, and finally bluish with increasing temperature. This occursbecause the wavelength associated with the peak radiation of theblack-body radiator becomes progressively shorter with increasedtemperature, consistent with the Wien Displacement Law. Illuminants thatproduce light which is on or near the black-body locus 15 can thus bedescribed in terms of their correlated color temperature (“CCT”). Asused herein, the term “white light” refers to light that is perceived aswhite, is within 7 MacAdam ellipses of the black-body locus on a 1931CIE chromaticity diagram, and has a CCT ranging from 2000K to 10,000K.White light with a CCT of 4000K may appear yellowish in color, whilewhite light with a CCT of 8000K or more may appear more bluish in color,and may be referred to as “cool” white light. “Warm” white light may beused to describe white light with a CCT of between about 2500K and4500K, which is more reddish or yellowish in color. Warm white light isgenerally a pleasing color to a human observer. Warm white light with aCCT of 2500K to 3300K may be preferred for certain applications.

The ability of a light source to accurately reproduce color inilluminated objects is typically characterized using the color renderingindex (“CRI”). The CRI of a light source is a modified average of therelative measurements of how the color rendition of an illuminationsystem compares to that of a reference black-body radiator whenilluminating eight reference colors. Thus, the CRI is a relative measureof the shift in surface color of an object when lit by a particularlamp. The CRI equals 100 if the color coordinates of a set of testcolors being illuminated by the illumination system are the same as thecoordinates of the same test colors being irradiated by the black-bodyradiator. Daylight generally has a CRI of nearly 100, incandescent bulbshave a CRI of about 95, fluorescent lighting typically has a CRI ofabout 70 to 85, while monochromatic light sources have a CRI ofessentially zero. Light sources for general illumination applicationswith a CRI of less than 50 are generally considered very poor and aretypically only used in applications where economic issues preclude otheralternatives. Light sources with a CRI value between 70 and 80 haveapplication for general illumination where the colors of objects are notimportant. For some general interior illumination, a CRI value ofgreater than 80 is acceptable. A light source with color coordinateswithin 4 MacAdam step ellipses of the planckian locus 15 and a CRI valuethat exceeds 85 is more suitable for general illumination purposes.Light sources with CRI values of more than 90 provide greater colorquality.

For backlight, general illumination and various other applications, itis often desirable to provide a lighting source that generates whitelight having a relatively high CRI, so that objects illuminated by thelighting source may appear to have more natural coloring to the humaneye. Accordingly, such lighting sources may typically include an arrayof semiconductor lighting devices including red, green and blue lightemitting devices. When red, green and blue light emitting devices areenergized simultaneously, the resulting combined light may appear white,or nearly white, depending on the relative intensities of the red, greenand blue sources. However, even light that is a combination of red,green and blue emitters may have a low CRI, particularly if the emittersgenerate saturated light, because such light may lack contributions frommany visible wavelengths.

CRI is an average color rendering value for eight specific sample colorsthat are generally referred to as R1-R8. Additional sample colors R9-R15are also often used in evaluating the color rendering properties of alight source. The sample color R9 is the saturated red color, and it isgenerally known that the ability to reproduce red colors well isimportant for accurately rendering colors, as the color red is oftenfound mixed into processed colors. Accordingly, all else being equal,lamps with high R9 values tend to produce the most vivid colors. Thus,the CRI R9 value of light emitted by a light source is also oftenconsidered to be an important performance parameter for a light source.

Another important performance parameter for an LED lighting source isthe intensity of the light emitted, which is referred to as the “radiantflux” of the device. However, as the human eye has varying sensitivityto different wavelengths of light, the intensity of the light emitted bya lighting source is most typically measured in terms of the lightingsource's “luminous flux,” which is a measure of the power of the lightemitted by a light source as perceived by a human observer. The luminousflux of a light source is typically measured in lumens (lm). Theluminous flux of a light source differs from the radiant flux of thelight source in that the radiant flux measures the total power emitted,while the luminous flux weights the power of the light emitted at eachwavelength based on a luminosity function which represents the responseof the human eye for each different wavelength.

FIG. 2 is a graph of the above-referenced luminosity function thatcorresponds to the response of the human eye to light in the visiblelight spectrum. As shown in FIG. 2, the human eye cannot perceive lightat wavelengths below about 400 nanometers and above about 700nanometers. The maximum response of the human eye to light occurs atabout 555 nanometers. In calculating luminous flux, the radiant flux ofa light source is weighted based on the eye sensitivity curve of FIG. 2.As the amount of light emitted by an LED is generally a function of thepower input to the LED, the luminous flux performance of semiconductorlight emitting devices are typically compared with each device beingdriven at the same input power level or, alternatively, the devices maybe compared in terms of the luminous flux per unit of input power (e.g.,lumens per Watt) that each device emits at the input power level forwhich each device is designed to operate.

Because of the varying sensitivity of the human eye to light ofdifferent wavelengths, there tends to be a tradeoff between the luminousflux of the light emitted by an LED lighting source and the CRI of thelight emitted. For example, since the human eye is most sensitive tolight at a wavelength of about 555 nm, a monochromatic light source at555 nm would exhibit a high luminous flux value. However, in order toobtain high CRI values, it is generally necessary to have lightcontribution across a wide range of wavelengths, including wavelengthsthat are relatively far away from 555 nm where the peak sensitivity oflight to the human eye occurs. This is particularly true with respect toCRI R9 performance which is a measure of color rendering in the redcolor range. Because the human eye has reduced sensitivity to thewavelengths on either end of the visible light spectrum, the lightcontributions that are often added to improve the CRI of a device mayresult in a decrease in the luminous flux of the device.

Embodiments of the present invention include semiconductor lightemitting devices that have recipient luminophoric mediums that includeluminescent materials that have peak emission wavelengths in variouscolor ranges. For purposes of this disclosure, the various color rangesof visible light are defined as shown in Table 1 below. It will beappreciated, however, that there are not sharp boundaries betweendifferent colors of the spectrum. For example, light having wavelengthsfrom 430-450 nm may appear blue-violet, while light having wavelengthsfrom 540-560 nm may appear yellow-green, etc.

TABLE 1 Color Wavelength Range (nm) Blue 440-479 Cyan 480-510 Green511-549 Yellow 550-580 Orange 581-604 Red 605-700

An LED or a luminescent material that emits light having a peakwavelength in one of the above color ranges may be referred to withreference to the color range. By way of example, a phosphor that emitslight having a peak wavelength of 630 nanometers may be referred toherein as a “red phosphor,” while a phosphor that emits light having apeak wavelength of 535 nanometers may be referred to as a “greenphosphor.”

Phosphors and other luminescent materials may, when excited, emit lightover a broad range of wavelengths or over a narrower range ofwavelengths. Herein, phosphors having emission spectrums that have FWHMwidths of 70 nanometers or more are referred to as “broad-spectrum” or“broadband” phosphors or luminescent materials. In contrast, luminescentmaterials that, when excited, emit light having FWHM widths of 60nanometers or less are referred to “narrow-spectrum” or “narrowband”luminescent materials.

FIG. 3 is a graph illustrating the intensity of the radiation emitted asa function of wavelength (i.e., the emission spectrum) for aconventional state-of-the-art warm white semiconductor light emittingdevice that includes a first broad-spectrum green Lu₃Al₅O₁₂:Ce phosphor(herein referred to as a “LuAG:Ce phosphor”) having a peak wavelengthbetween 530-540 nanometers, a second broad-spectrum red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a peak wavelength between620 and 640 nanometers, and a third broad-spectrum red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a peak wavelength between640 and 660 nanometers.

As shown in FIG. 3, the emission spectrum for the above-describedconventional state-of-the-art warm white semiconductor light emittingdevice has a small peak around 450 nanometers that corresponds to thelight emitted by the blue LED that passes through the recipientluminophoric medium without being absorbed by the phosphors. Theemission spectrum further includes a broad peak at around 635 nanometershaving a higher radiant flux than the small peak in the blue colorrange.

U.S. Pat. No. 8,921,875 (“the '875 patent”) proposes other white lightemitting semiconductor light emitting devices which each may include agreen and/or yellow phosphor, a broad-spectrum red phosphor and anarrow-spectrum red phosphor. The '875 patent explains that redphosphors generally can be classified into two categories, namely stableand unstable phosphors. The more unstable red phosphors are BOSE,sulfides and other non-nitride phosphors, while the more stable redphosphors are nitride-based phosphors such as the above-referenced(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. The nitride-based red phosphorsare typically characterized by broad emission spectrums (e.g., FWHMwidths of greater than 80 nm) and relatively high peak wavelengths(e.g., between about 630 nm and about 660 nm)

The '875 patent teaches that nitride-based red phosphors that have lowerpeak wavelengths (e.g., between about 610 nm and about 629 nm) andgenerally narrower emission spectrum (e.g., FWHM widths of between 60 nmand 80 nm) may be used in place of the above-described higher peakwavelength nitride-based red phosphors to provide improved performance.In particular, the '875 patent teaches that the use of lower peakwavelength red phosphors reduce the Stoke's shift (i.e., the differencebetween the peak wavelength of the light absorbed by the phosphor andthe peak wavelength of the light emitted by the phosphor), which isbeneficial as large Stoke's shift values can limit the conversionefficiency of a phosphor (i.e., the percentage of incident light that isabsorbed by the phosphor that is actually converted to light that isoutput by the phosphor). The '875 patent further explains thatnarrow-spectrum luminescent materials may be used as a means of fillingin gaps in the emission spectrum such as, for example, a gap that mayappear between the peak emission wavelength of a yellow phosphor and thepeak emission wavelength of a broad-spectrum red phosphor.

Pursuant to embodiments of the present invention, semiconductor lightemitting devices are provided that emit white light at significantlyhigher luminous flux levels (for a fixed amount of input power) withoutsacrificing performance in terms of color rendering or the color pointof the device. In some embodiments, the semiconductor light emittingdevices according to embodiments of the present invention may provide anincrease in luminous flux of 10% or more as compared to conventionalstate-of-the-art semiconductor light emitting devices.

In some embodiments, the semiconductor light emitting devices mayinclude one or more LEDs and a recipient luminophoric medium thatincludes a first luminescent material that emits light having a peakwavelength in the green or yellow color ranges, and second, third andfourth luminescent materials that each emit light having peakwavelengths in the red color range. In some embodiments, the second andthird luminescent materials may be broad-spectrum luminescent materialsthat have FWHM bandwidths of at least 70 nanometers, while the fourthluminescent material may be a narrow-spectrum luminescent material thathas a FWHM bandwidth of less than 60 nanometers. The peak wavelength ofthe fourth narrow-spectrum luminescent material may be between the peakwavelengths of the second and third broad-spectrum luminescentmaterials.

In some embodiments, the peak wavelengths of the light emitted by thesecond and third luminescent materials may be within 40 nanometers ofeach other or less (e.g., 35, 30, 25 or 20 nanometers in variousembodiments), and hence the peak wavelengths of all three red lightemitting luminescent materials may be tightly clustered within a narrowwavelength range. The amounts of the three red luminescent materialsincluded in the recipient luminophoric medium may be selected so thatthe emission of the semiconductor light emitting device in the 650-700nanometer range is reduced as compared to many conventionalstate-of-the-art semiconductor light emitting devices in order toincrease the luminous flux of the device.

In some embodiments, the second and third luminescent materials may bebroad-spectrum luminescent materials and may have a combined spectraloutput (in response to light emitted by the blue LED) that has a peakwavelength that is in the red color range. In some such embodiments, thefourth narrow-spectrum red luminescent material may have a peakwavelength that is within 5 to 20 nanometers of the peak wavelength ofthe combined spectral output of the second and third broad-spectrum redluminescent materials. This approach non-intuitively concentrates thelight emitted by the three red luminescent materials in a relativelynarrow range, yet still provides a combined light output that hasextremely high luminous flux while maintaining excellent color renderingproperties.

In other embodiments, semiconductor light emitting devices are providedthat includes one or more blue LEDs and an associated recipientluminophoric medium that has the above-described first through fourthluminescent materials and that have an emission spectrum that includes afirst peak at the peak wavelength of the fourth narrow-spectrum redluminescent material that is at least 50% greater than any point in theemission spectrum within the green or yellow color ranges. In otherwords, in these embodiments, the spectral output power of thesemiconductor light emitting device at the peak wavelength of the fourthnarrow-spectrum red luminescent material is significantly greater thanthe spectral output power within the green and yellow color ranges,which are the color ranges that are best perceived by the human eye.

In still other embodiments, semiconductor light emitting devices areprovided that includes one or more blue LEDs and an associated recipientluminophoric medium that has the above-described first through fourthluminescent material, where the fourth luminescent material emits lightthat has multiple distinct peaks in the red color range. In theseembodiments, a first of the multiple distinct peaks may be at awavelength that is less than a peak wavelength of a combined spectraloutput of the second and third luminescent materials in response to therespective second and third portions of the radiation emitted by theLED, and a second of the multiple distinct peaks is at a wavelength thatis greater than a peak wavelength of the combined spectral output of thesecond and third luminescent materials in response to the respectivesecond and third portions of the radiation emitted by the LED. The firstand second of the multiple distinct peaks may be the peaks in theemission spectrum of the fourth luminescent material that have thehighest spectral output power.

In yet additional embodiments, semiconductor light emitting devices areprovided that includes one or more blue LEDs and an associated recipientluminophoric medium that has a first luminescent material that emitslight having a first peak wavelength in the green or yellow colorranges, a second broad-spectrum luminescent material that emits lighthaving a second peak wavelengths in the red color range, and a thirdA₂MF₆:Mn⁴⁺ phosphor, where A is an Alkali metal and M is an element witha 4+ valence (e.g., a K₂SiF₆:Mn⁴⁺ phosphor) that emits light having athird peak wavelengths in the red color range. The second and third peakwavelengths may be within twenty (20) nanometers of each other.

In still further embodiments, semiconductor light emitting devices areprovided that include one or more blue LEDs and an associated recipientluminophoric medium that includes a first luminescent material thatdown-converts a first portion of the radiation emitted by the LED toradiation having a first peak wavelength that is in the green or yellowcolor ranges; a second luminescent material that down-converts a secondportion of the radiation emitted by the LED to radiation having a secondpeak wavelength that is in the red color range, the second luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers; and a third luminescent material that down-converts a thirdportion of the radiation emitted by the LED to radiation having a thirdpeak wavelength that is in the red color range and that is higher thanthe second peak wavelength, the third luminescent material having afull-width half maximum bandwidth of less than 60 nanometers. In thesedevices, the second peak wavelength is within twenty (20) nanometers ofthe third peak wavelength. In some embodiments, the third luminescentmaterial may be a K₂SiF₆:Mn⁴⁺ phosphor having a peak wavelength between630 and 640 nm, and the second luminescent material may be a(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a peak wavelength between610 and 630 nm.

In yet other embodiments, semiconductor light emitting devices areprovided that include one or more blue LEDs and a recipient luminophoricmedium that includes at least a YAG:Ce phosphor; a(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that emits light having a peakwavelength that is between 610 and 635 nm; and an A₂MF₆:Mn⁴⁺ phosphorwhere A is an Alkali metal and M is an element with a 4+ valence thatemits light having a peak wavelength that is between 625 and 640 nm, theA₂MF₆:Mn⁴⁺ phosphor having an emission peak that has a full-width halfmaximum bandwidth of less than 25 nm. The emission peak of theA₂MF₆:Mn⁴⁺ phosphor is between 625 and 640 nm and that has a full-widthhalf maximum bandwidth of less than 25 nm may be one of multipleemission peaks. In cases where the A₂MF₆:Mn⁴⁺ phosphor has multipleemission peaks, the peak that is between 625 and 640 nm and that has afull-width half maximum bandwidth of less than 25 nm may be the highestpeak in some embodiments. In these devices, the peak wavelength of the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor is within twenty (20) nanometers ofthe peak wavelength, of the A₂MF₆:Mn⁴⁺ phosphor, and the device may emitlight having a CRI value of between 80 and 92, a CRI R9 value of between30 and 70, a correlated color temperature of between 2700 K and 2850 K,and a Qg value (which is defined below) of between 90 and 110.

Additionally, pursuant to further embodiments of the present invention,methods of manufacturing the above described semiconductor lightemitting devices are provided, as well as methods for synthesizing thenarrow-spectrum red luminescent materials that may be used in someembodiments of the semiconductor light emitting devices according toembodiments of the present invention.

Example embodiments of the present invention will now be discussed withreference to FIGS. 4-12.

White light emitting semiconductor light emitting devices are providedpursuant to embodiments of the present invention that exhibit increasedlumens/Watt output, high CRI values, good CRI R9 performance and goodcolor quality. One such semiconductor light emitting device 100 isschematically depicted in FIG. 4. As shown in FIG. 4, the semiconductorlight emitting device 100 includes an LED 110 and a recipientluminophoric medium 120. The LED may comprise, for example, a blue LED110 that emits light having a peak wavelength between, for example, 440nanometers and 475 nanometers. In some embodiments, the blue LED 110 mayemit light having a peak wavelength between 445 and 460 nanometers.

The recipient luminophoric medium 120 may include a plurality ofluminescent materials that are suspended, for example, in one or morebinder layers. In the depicted embodiment, the recipient luminophoricmedium 120 includes four phosphors, namely a first broad-spectrum greenLuAG:Ce phosphor having a peak wavelength between 530-540 nanometers, asecond broad-spectrum red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having apeak wavelength between 620 and 640 nanometers, a third broad-spectrumred (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a peak wavelengthbetween 640 and 660 nanometers, and a fourth narrow-spectrum redphosphor having a peak wavelength between 630 and 640 nanometers. Insome embodiments, the second and third broad-spectrum red phosphors mayeach have a FWHM width of about 70-100 nanometers, and may havedifferent calcium-to-strontium ratios to achieve the different peakwavelengths. In some embodiments, the first broad-spectrum greenphosphor and the second and third broad-spectrum red phosphors may bethe same phosphors included in the conventional state-of-the-art whitesemiconductor light emitting device that is discussed above withreference to FIG. 3, although the relative amounts of the second andthird broad-spectrum red phosphors may be varied based on the additionof the fourth narrow-spectrum red phosphor in the semiconductor lightemitting device 100 according to embodiments of the present invention.

In some embodiments, the second broad-spectrum red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a material compositionthat is configured to have an emission spectrum with a peak wavelengthof about 620-640 nanometers when excited by light having a wavelengthbetween 440 and 475 nanometers. For example, the second broad-spectrumred (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a europium content ofabout 0.02 to 0.03, and may have a strontium content of about 0.80 toabout 0.92. In one particular embodiment, the second broad-spectrum redphosphor may have a strontium concentration of about 0.87, a europiumconcentration of about 0.025, a calcium concentration of 0.105 and apeak wavelength of about 630 nanometers.

In some embodiments, the third broad-spectrum red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a material compositionthat is configured to have an emission spectrum with a peak wavelengthof about 640-660 nanometers when excited by light having a wavelengthbetween 440 and 475 nanometers. In particular, the third broad-spectrumred nitride phosphor may have a europium content of about 0.003 to0.015, and may have a strontium content of about 0.15 to about 0.3. Inone particular embodiment, the third broad-spectrum red phosphor mayhave a strontium concentration of about 0.20, a europium concentrationof about 0.006, a calcium concentration of 0.794 and a peak wavelengthof about 650 nanometers.

In some embodiments, the fourth narrow-spectrum red phosphor maycomprise an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkali metal and M is anelement with a 4+ valence. For example, in one particular embodiment,the fourth narrow-spectrum phosphor may comprise a K₂SiF₆:Mn⁴⁺ phosphor.

In the depicted embodiment, the first through fourth phosphors areincluded in separate layers 121-124. The first layer 121 that isfarthest from the LED 110 includes the first broad-spectrum greenphosphor, the second layer 122 that is second-farthest from the LED 110includes the second broad-spectrum red phosphor, the third layer 123that is the second closest to the LED 110 includes the thirdbroad-spectrum red phosphor, and the fourth layer 124 that is closest tothe LED 110 includes the fourth narrow-spectrum red phosphor. It will beappreciated that in other embodiments the luminescent materials may allbe mixed together in a single layer (or in two or three layers), or thatmore than four layers may be used. It will also be appreciated that theorder of the layers may be changed.

In some embodiments, the ratio, by weight, of the first green phosphorto the second, third and fourth red phosphors may be between 2:1 and3:1. The ratio, by weight, of the second and third red phosphors to thefourth red phosphor may be between 1:3 and 1:6. The ratio, by weight, ofthe second red phosphor to the third red phosphor may be between 3:1 and1:1.

FIG. 5 is a graph of the emission spectrum 130 for the warm whitesemiconductor light emitting device 100 according to embodiments of thepresent invention. For comparative purposes, the emission spectrum 132of the conventional warm white semiconductor lighting device of FIG. 3is also included in the graph of FIG. 5.

As shown in FIG. 5, the emission spectra 130, 132 for the twosemiconductor light emitting devices differ in several significant ways.First, the emission spectrum 130 for the semiconductor light emittingdevice 100 includes increased spectral output in wavelength ranges fromabout 500 nanometers to about 600 nanometers. As this increased spectraloutput is in the wavelength range that is most readily perceived by thehuman eye, this increase in spectral output can result in a significantincrease in the luminous flux for the device. Second, the emissionspectrum 130 for the semiconductor light emitting device 100 accordingto embodiments of the present invention includes two significant peaksin the red color range, the first at about 620 nanometers and the secondat about 635 nanometers. These spectral peaks may not contribute heavilyto the luminous flux of the device because they are narrow and at highwavelengths, but may improve the CRI and CRI R9 performance of thedevice by increasing the amount of spectral output in the red colorrange. Third, the emission spectrum 130 for the semiconductor lightemitting device 100 according to embodiments of the present inventionhas reduced spectral output for wavelengths from about 650 to 700nanometers as compared to the emission spectrum 132 for the conventionalsemiconductor light emitting device. While this results in a very slightdecrease in the luminous flux of the semiconductor light emitting device100, the human eye is not very sensitive to light in this wavelengthrange and hence the reduction in luminous flux is small, and is morethan offset by the increased spectral output in the 600-650 nanometerrange. The decrease in spectral output in the 650-700 nanometer rangealso reduces the CRI performance of the device, but this decrease isgenerally offset by the increased spectral output in the 600-650nanometer range. Thus, the semiconductor light emitting device 100according to embodiments of the present invention may provide improvedperformance as compared to the conventional semiconductor light emittingdevice.

The emission spectrum in FIG. 5 for the semiconductor light emittingdevice 100 according to embodiments of the present invention also hasseveral other interesting characteristics. For example, the power of thepeak emission in the red color range is twice as high (or more) than thepower of the peak emissions in the green and yellow color ranges. Asanother example, the peak wavelength of the fourth narrow-spectrum redphosphor (about 634 nanometers) is between the peak wavelengths of thesecond and third broad-spectrum red phosphors (which have peakwavelengths of 629 and 650 nanometers in the particular embodiment ofFIGS. 4-5). In some embodiments, the peak wavelength of the fourthnarrow-spectrum red phosphor is within 30 nanometers of both the peakwavelength of the second broad-spectrum red phosphor and the peakwavelength of the third broad-spectrum red phosphor, and hence the peakwavelengths of all three red phosphors may be tightly grouped. In otherembodiments, the peak wavelength of the fourth narrow-spectrum redphosphor may be within 25 nanometers or even within 20 nanometers ofboth the peak wavelength of the second broad-spectrum red phosphor andthe peak wavelength of the third broad-spectrum red phosphor. In fact,while not shown in FIG. 5, in one particular embodiment, the combinedspectral output of the second and third luminescent materials inresponse to the blue LED has a peak wavelength in the red color range at635 nanometers, which is within 1 nanometer of the peak wavelength (634nanometers) of the fourth narrow-spectrum red phosphor in response tothe blue LED. In different embodiments of the present invention, thepeak wavelength of the combined emission of the second and thirdbroad-spectrum red phosphors may be within 10, 20, 30 or 40 nanometersof the peak wavelength of the fourth narrow-spectrum red phosphor whenthe second and third broad-spectrum red phosphors are excited byemission from the blue LED.

In the emission spectrum of FIG. 5, the peak emission occurs at the peakwavelength of the fourth narrow-spectrum red luminescent material. Asshown in FIG. 5, this peak emission has a magnitude that is about twicethe magnitude of the emission at any wavelength in the blue, cyan, greenor yellow color ranges. The relative amounts of the variousphosphors/luminescent materials may be adjusted in other embodiments sothat the peak emission that occurs at the peak wavelength of the fourthnarrow-spectrum red luminescent material is at least 1.5 times as high,at least 1.75 times as high, at least 2.5 times as high, or even atleast 3.0 times as high as the magnitude of the emission at anywavelength in the blue, cyan, green and/or yellow color ranges. It willalso be appreciated that in these additional embodiments the firstphosphor may be a green phosphor or a yellow phosphor, the secondphosphor may be a broad-spectrum red phosphor, and the third phosphormay be a broad-spectrum red phosphor, a narrow-spectrum red phosphor, oromitted altogether. It will further be appreciated that in any of theabove-described embodiments the green phosphor may be replaced with ayellow phosphor or both a green phosphor and a yellow phosphor may beincluded in the recipient luminophoric medium.

FIGS. 6A-6D are graphs that compare the performance of the conventionalsemiconductor light emitting device having the emission spectrum shownin FIG. 3 and the semiconductor light emitting device 100 according toembodiments of the present emission that is discussed above withreference to FIGS. 4-5. In particular, FIGS. 6A-6D compare the devicesin terms of their luminous flux, color rendering index (“CRI”)performance, CRI R9 performance and color point. In FIGS. 6A-6C, thedata points are spread out slightly along the horizontal axis so thatindividual data points can be distinguished more clearly.

FIG. 6A is a graph that shows the measured luminous flux for tensemiconductor light emitting devices 100 according to embodiments of thepresent invention as compared to eleven of the above-describedconventional semiconductor light emitting devices. All of the lightemitting devices were powered at the same input power level ingenerating the graph of FIG. 6A. As shown in FIG. 6A, on average, thesemiconductor light emitting devices 100 according to embodiments of thepresent invention exhibited luminous flux levels that were about tenpercent higher than the conventional semiconductor light emittingdevices. This represents a significant increase in luminous flux.

FIG. 6B shows the CRI performance for the twenty-one semiconductor lightemitting devices used to generate FIG. 6A. As shown in FIG. 6B, the CRIperformance is almost identical, with the conventional semiconductorlight emitting devices exhibiting an average CRI of about 90.5 and thesemiconductor light emitting devices 100 according to embodiments of thepresent invention exhibiting an average CRI value of about 90.4.

FIG. 6C shows the CRI R9 performance for the twenty-one semiconductorlight emitting devices used to generate FIG. 6A. As shown in FIG. 6C,the CRI R9 performance of the two semiconductor light emitting devicedesigns is also almost identical, with the conventional semiconductorlight emitting devices exhibiting an average CRI R9 value of about 54,while the semiconductor light emitting devices 100 according toembodiments of the present invention exhibit an average CRI R9 value ofabout 53.

Finally, FIG. 6D shows the actual color point of each of the twenty-onesemiconductor light emitting devices used to generate FIG. 6A. As shownin FIG. 6D, all of the semiconductor light emitting devices have colorpoints falling in the same color bin and there is no discernibledifference in the color points of the two different semiconductor lightemitting device designs. The correlated color temperatures of thesemiconductor light emitting devices used to generate FIG. 6D arebetween 2890K and 3070K, and hence all of the semiconductor lightemitting devices emit warm white light. FIGS. 6A-6D show that thesemiconductor light emitting devices 100 according to embodiments of thepresent invention may provide a significant (e.g., 10%) increase inluminous flux while maintaining the same color point and color renderingperformance.

As noted above, in some embodiments, the fourth narrow-spectrum redluminescent material may comprise an A₂MF₆:Mn⁴⁺ phosphor, where A is anAlkali metal and M is an element with a 4+ valence (e.g., a K₂SiF₆:Mn⁴⁺phosphor). FIG. 7 is a graph illustrating the excitation and emissionspectra of a narrow-spectrum K₂SiF₆:Mn⁴⁺ red phosphor that may beincluded in semiconductor light emitting devices according toembodiments of the present invention. In FIG. 7, the dotted linerepresents the excitation spectrum and the solid line represents theemission spectrum of the K₂SiF₆:Mn⁴⁺ phosphor.

As shown in FIG. 7, the K₂SiF₆:Mn⁴⁺ phosphor may be excited by light intwo excitation wavelength ranges, namely a first range in theultraviolet color range that has a peak excitation at about 355nanometers, and a second range in the blue color range that has a peakexcitation at about 455 nanometers. The excitation is stronger in theblue color range, meaning that, for a blue light excitation source, lessphosphor is required to achieve the same amount of red light emission ascompared to a corresponding ultraviolet light excitation source.

As is also shown in FIG. 7, the K₂SiF₆:Mn⁴⁺ phosphor has a somewhatunique emission spectrum, with the phosphor emitting light in the redcolor range with as many as five distinct peaks in the emission spectrumthat are located at about 610, 615, 635, 640 and 650 nanometers. Thepeaks at about 610 and 640 nanometers are within the larger peaks atabout 615 and 635 nanometers, respectively. As can be seen in FIG. 7,the peaks are very small, with FWHM widths of about 2-15 nanometers.

It should be noted that characteristics of an emission spectrum such as“peak wavelength” and “FWHM width” may need special definitions in thecontext of luminescent materials that include multiple emission peakssuch as the emission spectrum shown in FIG. 7. For purposes of thisdisclosure, the peak wavelength of a multi-peak emission spectrum is thewavelength where the highest amount of radiant flux is output (e.g.,about 634 nanometers in the emission spectrum of FIG. 7), and the FWHMwidth of the emission spectrum is defined as the distance (innanometers) between the wavelength defining the lower boundary of theFWHM width of the individual peak having the lowest peak wavelength andthe wavelength defining the upper boundary of the FWHM width of theindividual peak having the highest peak wavelength. For example, in thecontext of the K₂SiF₆:Mn⁴⁺ phosphor having the emission spectrum shownin FIG. 7, the individual peak having the lowest peak wavelength has apeak wavelength of 615 nanometers and a FWHM width of 13 nanometers;thus the wavelength defining the lower boundary of the FWHM width of theindividual peak having the lowest peak wavelength is 608 nanometers.Likewise, the individual peak having the highest peak wavelength has apeak wavelength of 650 nanometers and a FWHM width of 5 nanometers; thusthe wavelength defining the upper boundary of the FWHM width of theindividual peak having the highest peak wavelength is 653 nanometers.The FWHM width of the phosphor is the difference between these twowavelengths, or 45 nanometers.

While in the above-described embodiments, the fourth narrow-spectrum redluminescent material comprises an A₂MF₆:Mn⁴⁺ phosphor where A is anAlkali metal and M is an element with a 4+ valence (e.g., a K₂SiF₆:Mn⁴⁺phosphor), it will be appreciated that in other embodiments differentnarrow-spectrum red luminescent materials may be used. Examples ofpotentially suitable narrow-spectrum red luminescent materials includeCd(Se,S) quantum dots, Zn(Se,S) quantum dots, AeLiAl₃N₄:Eu²⁺ phosphorsor SrMg₃SiN₄:Eu²⁺ phosphors, where Ae is an alkaline-earth element suchas calcium or strontium. Likewise, according to further embodiments ofthe present invention, one or both of the above-described(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors may be replaced with otherbroad-spectrum red luminescent materials such as, for example, aY₂O₃:Eu³⁺ phosphor, a Y₂O₂S:Eu³⁺ phosphor, a (Y,Bi)VO₄:Eu³⁺ phosphor, aLu₂O₃:Eu³⁺ phosphor, a (Sr_(2-x)La_(x))(Ce_(1-x)Eu_(x))O₄ phosphor, anSr₂Ce_(1-x)Eu_(x)O₄ phosphor, an Sr_(2-x)Eu_(x)CeO₄ phosphor, anSrTiO₃:Pr³⁺,Ga³⁺ phosphor and/or an Sr₂Si₅N₈:Eu²⁺ phosphor.Additionally, one of the two broad-spectrum red phosphors could bereplaced with a narrow-spectrum red phosphor in some embodiments. Whilethe green broad-spectrum luminescent material has primarily beendiscussed above with respect to LuAG:Ce, other suitable green lightemitting broad-spectrum luminescent materials may be used including, forexample, a gallium-substituted YAG:Ce phosphor(Y_(a)Al_(b)Ga_(c)O_(z):Ce), an Sr₆P₅BO₂₀:Eu phosphor, a MSi₂O₂N₂:Eu²⁺phosphor and/or a Zinc Sulfide:Ag with (Zn,Cd)S:Cu:Al phosphor, or othercombinations. A narrow-spectrum green phosphor could be used in place ofthe LuAG:Ce phosphor in some embodiments.

While the above-described embodiments of the present invention use anarrow-spectrum red luminescent material to provide semiconductor lightemitting devices having, for example, improved lumens/Watt performancefor a generally fixed CRI value, it will be appreciated that additionalnarrow-spectrum luminescent materials may be added to the recipientluminophoric medium that emit light in other color ranges. By way ofexample, pursuant to further embodiments of the present invention, anyof the above-described semiconductor light emitting devices may bemodified to further include a narrow-spectrum luminescent material thatemits light in, for example, the cyan or green color ranges. Theinclusion of one or more such additional narrow-spectrum luminescentmaterials in color ranges other than the red color range may, forexample, provide semiconductor light emitting devices having improvedCRI values. It will also be appreciated that any of the above-describedsemiconductor light emitting devices may be modified to further includeadditional broad-spectrum luminescent materials in the recipientluminophoric medium such as, for example, a broad-spectrum yellowphosphor.

FIGS. 8A-8D are cross-sectional diagrams illustrating examplesemiconductor light emitting devices according to embodiments of thepresent invention that include recipient luminophoric mediums having oneor more narrow-spectrum luminescent materials.

FIG. 8A illustrates a first semiconductor light emitting device 200 thatincludes an LED 210 and a recipient luminophoric medium 220. The LED 210included in device 200 would typically be a blue LED, although violet,ultraviolet or other LEDs could be used. As shown in FIG. 8A, therecipient luminophoric medium 220 is arranged to receive light emittedby the LED 210 including, for example, light emitted from the sides andtop of the LED 210. The recipient luminophoric medium 220 includes (1) afirst broad-spectrum luminescent material 221 that down-convertsradiation emitted by the LED 210 to radiation having a peak wavelengthin the green color range, (2) a second broad-spectrum luminescentmaterial 222 that down-converts radiation emitted by the LED 210 toradiation having a peak wavelength in the red color range, (3) a fourthnarrow-spectrum luminescent material 223 that down-converts radiationemitted by the LED 210 to radiation having a peak wavelength in the redcolor range, and (4) a third broad-spectrum luminescent material 224that down-converts radiation emitted by the LED 210 to radiation havinga peak wavelength in the red color range. The semiconductor lightemitting device 200 is similar to the semiconductor light emittingdevice 100 discussed above with reference to FIGS. 4-5, with the onlydifference being that the positions of the third broad-spectrum redluminescent material 123/224 and the fourth narrow-spectrum luminescentmaterial 124/223 are in reversed in the respective recipientluminophoric mediums 120/220.

FIG. 8B illustrates another semiconductor light emitting device 230 thatincludes the LED 210 and a recipient luminophoric medium 240. Therecipient luminophoric medium 240 is arranged to receive light emittedby the LED 210. The recipient luminophoric medium 240 includes the samefour luminescent materials 221-224 as the recipient luminophoric medium220 of LED 200, and additionally includes one additional luminescentmaterial in the form of a fifth broad spectrum yellow luminescentmaterial such as, for example, a Y₃Al₅O₁₂:Ce phosphor (which may bereferred to herein as a YAG:Ce phosphor). In the particular embodimentof FIG. 8B, the fifth yellow broad-spectrum luminescent material 245 isincluded in a separate layer between the first broad-spectrum greenluminescent material 221 and the second broad-spectrum red luminescentmaterial 222.

FIG. 8C illustrates another semiconductor light emitting device 250 thatincludes the LED 210 and a recipient luminophoric medium 260. Therecipient luminophoric medium 260 is arranged to receive light emittedby the LED 210. The recipient luminophoric medium 260 includes the samefour luminescent materials 221-224 as the recipient luminophoric medium220 of LED 200, and additionally includes one additional luminescentmaterial in the form of a fifth narrow-spectrum cyan luminescentmaterial 265 such as, for example, a Ba₂Si₂O₂N₂:Eu²⁺ phosphor or an(Sr,Ba,Ca)₂SiO₄:Eu²⁺ phosphor. In the particular embodiment of FIG. 8C,the fifth narrow-spectrum cyan luminescent material 265 is included in aseparate layer that is the farthest layer in the recipient luminophoricmedium 260 from the LED 210. The fifth narrow-spectrum cyan luminescentmaterial 265 may provide a device having an improved CRI value, as itmay emit light that fills in a gap in the emission spectrum between theblue peak generated by the blue LED 210 and the green peak generated bythe first broad-spectrum green phosphor 221.

It will be appreciated that FIGS. 8A-8C are not intended to be limiting.For example, while the recipient luminophoric mediums depicted in FIGS.8A-8C are shown as comprising multi-layer recipient luminophoric mediumswith each different phosphor included in its own layer, it will beappreciated that single layer recipient luminophoric mediums may be usedinstead in which all of the phosphors (or other luminescent materials)are mixed within the same layer or coating. Additionally, as shown inFIG. 8D, in other embodiments subsets of the various luminescentmaterials may be mixed in one or more layers of a multi-layer recipientluminophoric medium. In the example of FIG. 8D, a semiconductor lightemitting device 270 is provided that includes the LED 210 and arecipient luminophoric medium 280. The recipient luminophoric medium 280is a two layer recipient luminophoric medium in which the firstbroad-spectrum green luminescent material 221 is included in its ownlayer and the second broad-spectrum red luminescent material, the thirdbroad-spectrum red luminescent material and the fourth narrow-spectrumred luminescent material are mixed together in a second layer 282. Itwill be appreciated that numerous other variations are possible.

It will also be appreciated that other changes may be made to thesemiconductor light emitting devices 200, 230, 250, 270 of FIGS. 8A-8D.For example, in other embodiments, one or more of the layers of therecipient luminophoric mediums may not extend to surround side surfacesof the LEDs 210, and may not even cover an entire top (or other) surfaceof the LEDs 210. As another example, the recipient luminophoric mediumsneed not be coated directly on the respective LEDs 210, but instead needonly be arranged to receive light emitted by their respective LEDs 210.Additional broad-spectrum luminescent material(s) and/or narrow-spectrumluminescent material(s) may also be included in the depictedsemiconductor light emitting devices.

The above-described recipient luminophoric mediums that include a greenand/or yellow phosphor, two broad-spectrum red phosphors and anarrow-band spectrum red phosphor having a peak wavelength that isbetween the peak wavelengths of the two broad-spectrum red phosphors isa non-conventional approach that provides unexpected results. Asexplained, for example, in the above-described '875 patent, the use ofnarrow-spectrum luminescent materials has been suggested as a means offilling in gaps in the spectrum such as, for example, a gap that mayappear between the peak emission wavelength of a yellow phosphor and thepeak emission wavelength of a broad-spectrum red phosphor. However, theuse of such a narrow-spectrum red phosphor would not appear to be neededin a recipient luminophoric medium that included two broad-spectrum redphosphors that have relatively close peak wavelengths (i.e., peakwavelengths within a 35 nanometer range), as there would be little ifany dip in the spectral output of such a recipient luminophoric mediumin the region between the two peak wavelengths (in fact, as shown inFIG. 3, the peak wavelength of the light output by such a semiconductorlight emitting device may be between the peak wavelengths of the twobroad-spectrum red phosphors). However, it has been discovered by thepresent inventors that including a narrow-spectrum red phosphor in thisregion may actually provide significantly improved performance in termsof the luminous flux that is achieved for a given CRI performance level.Such a result is non-intuitive as the spectrum of light emitting devicesaccording to embodiments of the present invention may concentrate outputpower at wavelengths that are reasonably far down the eye sensitivitycurve. However, by further decreasing the output power at even longerwavelengths and by also increasing the output power in the centralportion of the eye sensitivity curve (e.g., by increasing the amount ofthe second broad-spectrum red phosphor that has the lower peakwavelength), improved performance may unexpectedly be achieved.

In some embodiments, the recipient luminophoric medium may include twobroad-spectrum red luminescent materials that have peak wavelengths thatare within 40 nanometers of each other. The recipient luminophoricmedium may further include a narrow-spectrum red luminescent materialthat has a peak wavelength that is between the peak wavelengths of thetwo broad-spectrum luminescent materials. In some embodiments, the twobroad-spectrum red luminescent materials may have peak wavelengths thatare within 35 nanometers of each other, 30 nanometers of each other, 25nanometers of each other, or even 20 nanometers of each other. In eachcase, the narrow-spectrum red luminescent material may have a peakwavelength that is between the peak wavelengths of the twobroad-spectrum luminescent materials.

In some embodiments, the two broad-spectrum red luminescent materialsmay have a combined spectral output that has a peak wavelength that isin the red color range. In some of these embodiments, thenarrow-spectrum red luminescent material may have a peak wavelength thatis within 20 nanometers of the peak wavelength of the combined spectraloutput of the two broad-spectrum red luminescent materials. In otherembodiments, the narrow-spectrum red luminescent material may have apeak wavelength that is within 15 nanometers of the peak wavelength ofthe combined spectral output of the two broad-spectrum red luminescentmaterials. In still other embodiments, the narrow-spectrum redluminescent material may have a peak wavelength that is within 10nanometers of the peak wavelength of the combined spectral output of thetwo broad-spectrum red luminescent materials.

In some embodiments, a semiconductor light emitting device is providedthat includes one or more LEDs and a recipient luminophoric medium thathas a first luminescent material that emits light having a peakwavelength in the green or yellow color ranges, and second, third andfourth luminescent materials that emit light having peak wavelengths inthe red color range, where the peak wavelength of the light emitted bythe fourth luminescent material is between the peak wavelengths of thelight emitted by the second and third luminescent materials. An emissionspectrum of the semiconductor light emitting device includes a firstpeak at the peak wavelength of the fourth luminescent material that isat least 50% greater than (i.e., 1.5 times as high as) any point in theemission spectrum in the green or yellow color ranges. In someembodiments, an emission spectrum of the semiconductor light emittingdevice may include a first peak at the peak wavelength of the thirdluminescent material that is at least 1.75 times as high, twice as high,or even three times as high as any point in the emission spectrum in thegreen or yellow color ranges.

In some embodiments, the narrow-spectrum luminescent material may havean emission spectrum that includes multiple peaks.

While the above examples describe using the recipient luminophoricmediums according to embodiments of the present invention to fabricatewarm white light emitting devices (e.g., color temperatures of 2500K to3300K), it will be appreciated that they can likewise be used tofabricate white light emitting devices that have other colortemperatures including, for example, white light emitting devices havingcorrelated color temperatures of between 3300K and 5500K.

It will be appreciated that various modifications may be made to theabove-described semiconductor light emitting devices and associatedrecipient luminophoric mediums without departing from the teachings ofthe present invention. For example, while the above-describedembodiments may provide excellent CRI performance, in some applications,lower CRI performance (e.g., a CRI of at least 80) may be fullyacceptable. In such applications, it may be possible to adjust thephosphor combination to increase the luminous flux of the semiconductorlight emitting device at the expense of reduced CRI performance.

In one example embodiment, a semiconductor light emitting device may beprovided that includes one or more LEDs (e.g., a blue LED that emitslight having a peak wavelength between 440 and 470 nanometers) and arecipient luminophoric medium that includes first through fourthluminescent materials. This semiconductor light emitting device mayhave, for example, the design of the semiconductor light emitting device100 of FIG. 4 that is discussed above except that the luminescentmaterials included in the recipient luminophoric medium 120 are modifiedas discussed below.

In particular, in this modified version of the semiconductor lightemitting device 100 of FIG. 4, the recipient luminophoric medium mayinclude a first luminescent material in the form of a LuAG:Ce phosphor,a second luminescent material in the form of a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has calcium and strontiumconcentrations that are selected so that the phosphor emits light inresponse to the blue LED having a peak wavelength between 610 and 620nanometers (e.g., a peak wavelength of 614 nanometers), a thirdluminescent material in the form of a second (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor that has a higher calcium concentration and a lower strontiumconcentration than the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor sothat the second (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor emits light inresponse to the blue LED having a peak wavelength between 621 and 630nanometers (e.g., a peak wavelength of 624 nanometers), and a fourthluminescent material in the form of an A₂MF₆:Mn⁴⁺ phosphor where A is anAlkali metal and M is an element with a 4+ valence (e.g., a K₂SiF₆:Mn⁴⁺phosphor having a peak wavelength of 634 nm).

In some embodiments, the second and third luminescent materials may havepeak wavelengths that are within 20 nanometers of each other. In otherembodiments, the second and third luminescent materials may have peakwavelengths that are within 15 nanometers of each other. In still otherembodiments (such as the specific embodiment discussed above where thesecond and third luminescent materials are (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphors having peak wavelengths of 614 and 624 nanometers), the secondand third luminescent materials may have peak wavelengths that arewithin 10 nanometers of each other. In each of the above-describedembodiments, the fourth luminescent material may have a peak wavelengththat is within 15 nanometers of the peak wavelength of the thirdluminescent material. In some cases (such as the specific embodimentdiscussed above where the third luminescent material has a peakwavelength of 624 nanometers and the fourth luminescent material has apeak wavelength of 634 nanometers), the fourth luminescent material mayhave a peak wavelength that is within 10 nanometers of the peakwavelength of the third luminescent material. In some embodiments, thepeak wavelength of the fourth luminescent material may be between thepeak wavelengths of the second and third luminescent materials, while inother embodiments the peak wavelength of the fourth luminescent materialmay exceed the peak wavelengths of both the second and third luminescentmaterials.

In specific example embodiments of the above-described recipientluminophoric mediums, a ratio of the first luminescent material to thesecond, third and fourth luminescent materials by weight may be between2:1 and 3:1, and a ratio of the second and third luminescent materialsto the fourth luminescent material by weight may be between 1:2 and 1:4.A ratio of the second luminescent material to the third luminescentmaterial by weight may be between 1:1 and 1:3. A ratio of the firstluminescent material to the second luminescent material by weight may bebetween 1:4 and 1:3, and the ratio of the first and the secondluminescent materials to the third luminescent material maybe between12:1 and 14:1.

The above-described semiconductor light emitting device may be designedto have CRI values of, for example, at least 80. These semiconductorlight emitting devices may exhibit higher luminous flux values ascompared to a state-of-the-art conventional 80 CRI semiconductor lightemitting device (specifically a semiconductor light emitting devicehaving a recipient luminophoric medium that includes a LuAG:Ce phosphor(having a peak wavelength of 535 nanometers, a YAG:Ce phosphor having apeak wavelength of 557 nm, and a red phosphor having a peak wavelengthof 629 nanometers). The above-described semiconductor light emittingdevice may exhibit lower CRI R9 values (e.g., by between 3 to 5 units)than the CRI R9 values for the state-of-the-art conventional 80 CRIsemiconductor light emitting device. FIG. 14 depicts the emissionspectrum for the above-described semiconductor light emitting deviceaccording to embodiments of the present invention (shown with the dottedline) as compared to the emission spectrum of the above describedstate-of-the-art conventional 80 CRI semiconductor light emitting device(shown with the solid line).

A semiconductor light emitting device will now be described thatincludes a recipient luminophoric medium according to embodiments of thepresent invention with reference to FIG. 9. In particular, FIG. 9 is aside schematic view of a light emitting device 300 that includes an LED310 that is mounted on a mounting surface 320. The LED 310 may comprise,for example, an LED that emits radiation having a dominant wavelength inthe blue color range (e.g., radiation with a dominant wavelength ofbetween 440 to 475 nanometers). A recipient luminophoric medium 330 isprovided that is positioned to receive light that is emitted by the LED310. The luminophoric medium 330 may comprise an encapsulant materialsuch as, for example, silicone that has luminescent materials suspendedtherein. In the embodiment pictured in FIG. 9, the recipientluminophoric medium 330 is conformally coated on an upper and sidesurfaces of the LED 310 and on the mounting surface 320 and sidewalls ofa reflector cup. It will be appreciated, however, that the recipientluminophoric medium 330 may be placed in other locations. For example,in other embodiments, the recipient luminophoric medium 330 may becoated on an interior and/or exterior surface of a lens 350, embodied asan encapsulant material 340 that is provided between the LED 310 and thelens 350 or in any other suitable location where the recipientluminophoric medium 330 may receive at least some of the light emittedby the LED 310 and convert at least some of the emitted light to lighthaving different wavelengths. The recipient luminophoric medium 330 maybe any of the above-described recipient luminophoric mediums accordingto embodiments of the present invention. The blue LED 310 is shown ashaving a topside contact, but may comprise a flip-chip LED in otherembodiments.

FIG. 10 is a perspective view of a semiconductor light emitting device400 according to further embodiments of the present invention. As shownin FIG. 10, the solid state light emitting device 400 includes asubstrate/submount (“submount”) 420 on which four LED chips or “die” 410are mounted. The submount 420 can be formed of many different materialssuch as, for example, aluminum oxide, aluminum nitride, organicinsulators, a printed circuit board (PCB), sapphire or silicon. The LEDs410 can have many different semiconductor layers arranged in differentways. LED structures and their fabrication and operation are generallyknown in the art and hence are only briefly discussed herein. The layersof the LEDs 410 can be fabricated using known processes such as, forexample, metal organic chemical vapor deposition. Typically, LEDs aregrown on a growth substrate such as, for example, a sapphire, siliconcarbide, aluminum nitride (AlN), or gallium nitride (GaN) substrate toprovide a grown semiconductor wafer, and this wafer is then singulatedinto individual LED dies 410. The growth substrate can remain as part ofthe final singulated LED or, alternatively, the growth substrate can befully or partially removed. In embodiments where the growth substrateremains, it can be shaped and/or textured to enhance light extraction.The LEDs 410 may be mounted in flip chip configuration in someembodiments.

The LEDs 410 may each include a conductive current spreading structure412 on the respective top surfaces thereof, as well as one or morecontacts 414 that are accessible at its top surface for wire bonding. Inother embodiments, one or both contacts 414 for each LED 410 may be on abottom side of the LED. The current spreading structure 412 and contacts414 can both be made of a conductive material such as Au, Cu, Ni, In,Al, Ag or combinations thereof, conducting oxides and transparentconducting oxides. The current spreading structure 412 may compriseconductive fingers that are arranged in a pattern on each LED 410 withthe fingers spaced to enhance current spreading from the contacts 414into the top surface of the LEDs 410. In operation, an electrical signalis applied to the contacts 414 through a wire bond, and the electricalsignal spreads through the fingers of the current spreading structure412 into the LED 410.

The LEDs 410 may be coated with a recipient luminophoric medium 430according to embodiments of the present invention. As discussed above,this recipient luminophoric medium 430 may, for example, include a firstbroad-spectrum green luminescent material, second and thirdbroad-spectrum red luminescent materials, and a fourth narrow spectrumred luminescent material, which may be mixed together and/or provided inseparate layers). It will be understood that the recipient luminophoricmedium 430 may comprise any of the recipient luminophoric mediumsdiscussed in the present application. The recipient luminophoric mediummay be coated on the two LEDS 410, and may also be coated on portions ofthe submount 420 such as, for example, portions between the LEDs 410.

The recipient luminophoric medium 430 may include a binder material, andmay have different concentrations or loading of phosphor materials inthe binder, with a typical concentration being in range of 40-80% byweight. In one embodiment, the phosphor concentration is approximately75% by weight, and may be generally uniformly dispersed throughout thebinder. In other embodiments the recipient luminophoric medium 430 cancomprise multiple layers of different concentrations or types ofphosphors (or other luminescent materials), and the multiple layers cancomprise different binder materials. One or more of the layers can beprovided without phosphors. For example, a first coat of clear siliconecan be deposited followed by phosphor loaded layers.

The recipient luminophoric medium 430 may be coated on the LEDs 410using many different methods. For example, in some embodiments, therecipient luminophoric medium 430 may be applied to semiconductor LEDwafers during the LED manufacturing process. Suitable methods for suchwafer level deposition are described in U.S. Patent Publication Nos.2008/0173884 and 2008/0179611, both entitled Wafer Level PhosphorCoating Method and Devices Fabricated Utilizing Method. Alternativelythe recipient luminophoric medium 430 may be coated on the LEDs 410using other methods such an electrophoretic deposition (EPD), with asuitable EPD method described in U.S. Patent Publication No.2007/0158668 entitled Close Loop Electrophoretic Deposition ofSemiconductor Devices. In still other embodiments, the recipientluminophoric medium 430 may be sprayed or otherwise applied to the LEDs410 after the LEDs 410 have been singulated and mounted on the mountingsubstrate 420. Numerous other techniques are known in the art and aresuitable for applying the recipient luminophoric mediums according toembodiments of the present invention.

An optical element or lens 440 is formed over at least part of the topsurface of the submount 420 to enclose the LEDs 410 and provide bothenvironmental and/or mechanical protection therefore. The lens 440 canbe molded using different molding techniques such as those described inU.S. Patent Publication No. 2009/0108281 entitled Light Emitting DiodePackage and Method for Fabricating Same. The lens 440 can be manydifferent shapes such as, for example, hemispheric. Many differentmaterials can be used for the lens 440 such as silicones, plastics,epoxies or glass. The lens 440 can also be textured to improve lightextraction. In some embodiments, the lens 440 may comprise the recipientluminophoric medium 430 and/or may be used to hold a luminophoric medium430 in place over the LEDs 410 instead of and/or in addition to coatinga luminophoric medium 430 directly onto the LED chips 410.

The recipient luminophoric mediums according to embodiments of thepresent invention may also be applied to a light emitting device whilethe light emitting device is exposed to a curing agent. The curing agentmay be, for example, heat, radiation, a material that is present on orin the light emitting device, or other agents that speed up the curingof the recipient luminophoric medium.

Pursuant to further embodiments of the present invention, methods ofsynthesizing narrow-spectrum red phosphors are provided, as well asrelated methods of fabricating light emitting devices that include suchphosphors. FIG. 11 is a schematic diagram that illustrates certain ofthese methods according to embodiments of the present invention.

As shown in FIG. 11, the method may begin by dissolving MO₂ powder,which is commercially available for purchase, in a hydrofluoric acid(HF) solution in a first container 500. M may comprise any of Si, Ge,Sn, Ti, Zr or Hf. In some embodiments, M may be Si. The hydrofluoricacid solution may comprise, for example, a solution including 49%hydrofluoric acid and 51% water (HF/H₂O). The MO₂ powder may bedissolved in the hydrofluoric acid solution until no visible solidsremain. In some embodiments, this may require dissolving the MO₂ powderfor at least four hours in the hydrofluoric acid solution.

Next, an appropriate amount of A₂MnF₆ powder is added to the solutioncomprising MO₂ dissolved in the hydrofluoric acid solution. A maycomprise an Alkali metal such as, for example, potassium (K). The A₂MnF₆powder is dissolved in the solution and thoroughly mixed to provide anMO₂+A₂Mn₆F₂+HF/H₂O+MF solution.

In a second container 510, AHF₂ is dissolved in another hydrofluoricacid solution that may comprise, for example, 49% hydrofluoric acid and51% water, where A is the same Alkali metal (e.g., K) to provide anAHF₂+HF/H₂O solution. Next, the resulting AHF₂+HF/H₂O solution is thenadded to the MO₂+A₂Mn₆F₂+HF/H₂O+MF solution in the first container 500.The AHF₂+HF/H₂O solution may be added in a dropwise fashion, and may beadded at an elevated temperature. For example, in some embodiments, theAHF₂+HF/H₂O solution may be added to the MO₂+A₂Mn₆F₂+HF/H₂O+MF solutionat a temperature of between 40° C. and 90° C. When the two solutions arecombined, solid precipitates of A₂MF₆:Mn⁴⁺ form in the solution. Thesolution may then be decanted to remove the A₂MF₆:Mn⁴⁺ precipitates,which may then be washed in methanol. While not pictured in FIG. 11, inother embodiments, the MO₂+A₂Mn₆F₂+HF/H₂O+MF solution in the firstcontainer is added dropwise to the AHF₂+HF/H₂O solution instead of theother way around, which may provide improved results in some cases.

In some cases, further processing steps may be performed which may, forexample, improve the stability of the A₂MF₆:Mn⁴⁺ phosphor. Inparticular, as shown in FIG. 12, the synthesized A₂MF₆:Mn⁴⁺ phosphorprecipitates are added to a saturated A⁺+M⁴⁺+HF/H₂O (49% HF) solution ina third container 520. In a fourth container 530, AF is dissolved inanother hydrofluoric acid solution that may comprise, for example, 49%hydrofluoric acid and 51% water. The AF+HF/H₂O (49% HF) solution is thenadded dropwise to the A⁺+Mn⁴⁺+HF/H₂O (49% HF) solution that contains thepreviously synthesized A₂MF₆:Mn⁴⁺ phosphor precipitates. This results ina transparent coating of solid A₂MF₆ (without any Mn) on top of theA₂MF₆:Mn⁴⁺ phosphor particles. The solution may then be decanted and theprecipitates may be washed in methanol. This method reduces theconcentration of Mn⁴⁺ on the surface of the phosphor particles. Thismakes the phosphor particles less susceptible to degradation in humidenvironments.

The above-described method of synthesizing a narrow-spectrum A₂MF₆:Mn⁴⁺red phosphor may provide phosphor particles having a high degree ofpotency. The potency of a phosphor relates to the amount of phosphorthat must be provided to achieve a certain amount of emission from thephosphor for a fixed amount of excitation light. The more potent aphosphor, the less the amount of phosphor is required to achieve thedesired emission. Generally speaking, high potency is a desirableproperty for phosphors used in semiconductor light emitting devices, asthe smaller number of phosphor particles that may be required with highpotency phosphors may reduce absorption and scattering losses.

According to further embodiments of the present invention, semiconductorlight emitting devices may be provided that include recipientluminophoric mediums that include a first broad-spectrum green or yellowluminescent material and a fourth narrow-spectrum luminescent material,and one but not both of a second broad-spectrum red luminescent materialor a third broad-spectrum red luminescent material. In each suchsemiconductor light emitting device, the fourth narrow-spectrum redluminescent material may comprise an A₂MF₆:Mn⁴⁺ red phosphor, where A isan Alkali metal and M is Si, Ge, Sn, Ti, Zr or Hf. As an example, theselight emitting devices may have the structure of the semiconductor lightemitting device 200 that is shown in FIG. 8A with either the secondbroad-spectrum red phosphor 222 or the third broad-spectrum red phosphor223 omitted. In some such embodiments, the peak wavelength of theA₂MF₆:Mn⁴⁺ red phosphor may be within 26 nanometers of the peakwavelength of the broad-spectrum (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ redphosphor that is included in the device.

Pursuant to still further embodiments of the present invention, methodsof forming a semiconductor light emitting device are provided. FIG. 13is a flow chart illustrating the operations according to some of thesemethods.

As shown in FIG. 13, operations may begin with synthesizing anarrow-spectrum red phosphor by first dissolving MO₂ powder in a firsthydrofluoric acid solution to provide an MO₂+HF solution, where M is oneor more of Si, Ge, Sn, Ti, Zr or Hf (block 600). Next, dissolved A₂MnF₆is added to the MO₂+HF solution to provide a A₂MnF₆+MO₂+HF solution,where A is an Alkali metal (block 610). AHF₂ is dissolved in a secondhydrofluoric acid solution to provide an AHF₂+HF solution (block 620).This operation may be done before, after or concurrently with theoperations of blocks 600 and/or 610. Next, the AHF₂+HF solution is addedto the A₂MnF₆+MO₂+HF solution (block 630). In some embodiments, theAHF₂+HF solution may be added to the A₂MnF₆+MO₂+HF solution at atemperature between 40° C. and 90° C. Next, solid precipitates ofA₂MF₆:Mn⁴⁺ may be extracted from the combination of the AHF₂+HF and theA₂MnF₆+MO₂+HF solutions (block 640).

An LED is also provided (block 650). A recipient luminophoric mediumthat is configured to down-convert at least some of the light emitted bythe LED is also provided (block 660). The recipient luminophoric mediumincludes (1) a first luminescent material that down-converts a firstportion of the radiation emitted by the LED to radiation having a firstpeak wavelength in the green or yellow color ranges, (2) a secondluminescent material that down-converts a second portion of theradiation emitted by the LED to radiation having a second peakwavelength in the red color range, the second luminescent materialhaving a full-width half maximum bandwidth of at least 70 nanometers,(3) a third luminescent material that down-converts a third portion ofthe radiation emitted by the LED to radiation having a third peakwavelength in the red color range, and (4) a fourth luminescent materialthat includes the A₂MF₆:Mn⁴⁺ precipitates, the fourth luminescentmaterial configured to down-convert a fourth portion of the radiationemitted by the LED to radiation having a fourth peak wavelength in thered color range.

In some embodiments, M is silicon (Si) and A is potassium (K). Thefourth peak wavelength may be greater than the second peak wavelengthand less than the third peak wavelength. The second peak wavelength maybe within 30 nanometers of the third peak wavelength. An emissionspectrum of the semiconductor light emitting device may include a firstpeak at the fourth peak wavelength that is at least 50% greater than anypoint in the emission spectrum in the yellow or green color ranges.

Pursuant to further embodiments of the present invention, semiconductorlight emitting devices are provided that emit white light at highluminous flux values that may also have high CRI values, high CRI R9values, and high color quality. While CRI is often used as a measure ofthe quality of the color of a white light emitting device, CRI, at leaststanding alone, may not always provide a satisfactory measure of thecolor quality. In particular, the eight color samples that are used tocalculate CRI are primarily pastel shades, as opposed to saturatedcolors. As such, light emitting devices that emit light having high CRIvalues may still fall short in rendering certain hues such as red hues.As it turns out, the red content of a light source may be important foraccurately rendering colors of various foods, skin tones, wood,furniture and other objects, as only a few of the color samples used tocompute CRI have significant red content (namely sample R1, which is apink shade, and sample R8, which is a purple shade), and these samplesare not saturated color samples so that high CRI scores may be achievedeven without significant red content in a light source.

Seven additional color samples labelled CRI R9-R15 have been definedthat measure the color rendering of a light source for either saturatedcolors (R9-R12, corresponding to saturated red, yellow, green and bluelight) or for other colors (R13-R15) corresponding to two different skintones and leaf green. These color samples are not used in calculatingCRI, which is based solely on color samples R1-R8, but may be importantwhen evaluating the color rendering of a particular light source.

As discussed above, of these seven additional color samples, the CRI R9color sample is often considered the most important, given theprominence of the color red. Since color sample R9 corresponds to asaturated color, there is no way to achieve a high R9 score without asignificant red content in the light source. This can be seen in FIG.15, which shows the reflectance spectra (i.e., reflected power as afunction of wavelength) for the R1-R9 color samples when illuminated bya reference light source. As can be seen in FIG. 15, color samples R1-R8include mixes of many different colors, as shown by the fact thatsamples R1-R8 have significant contribution across a broad portion ofthe visible light spectrum, whereas color sample R9 includes very highspectral reflectivity in the red region with virtually no reflectivitybelow 600 nm. Thus, the R9 color sample may provide a very goodindicator of a light source's ability to accurately render the color ofred objects, and for this reason is often considered along with CRI inevaluating the quality of the color of a light source.

In addition, CRI also confers limited ability to predict colordiscrimination (i.e., to perceive subtle difference in hue) or colorpreference. There appears to be a natural human attraction to brightercolor. Daylight provides a spectrum of light that allows the human eyeto perceive bright and vivid colors, which allows a human observer todistinguish objects having even very subtle color shade differences.Accordingly, it is generally recognized that daylight and blackbodysources are superior to many artificial light sources for emphasizingand distinguishing color. The ability of human vision to differentiatecolor is different under correlated color temperature conditionsproviding the same CRI. Such differentiation is proportional to thegamut area of the illuminating light.

The gamut area of a light source can be calculated as the area enclosedwithin a polygon defined by the chromaticities in CIE 1976 u′v′ colorspace of the eight color samples R1-R8 used to calculate CRI whenilluminated by a test light source. Gamut area index (GAI) is aconvenient way of characterizing in chromaticity space how saturated theillumination makes objects appear, with a larger GAI making objectcolors appear more saturated. GAI is a relative number whereby animaginary equal-energy spectrum (wherein radiant power is equal at allwavelengths) is scored as 100. GAI for a test source is determined bycomparing color space area of the light being tested to the color spacearea produced by the imaginary or theoretical equal-energy spectrum(EES) source. Unlike CRI, which has a maximum value of 100, GAI canexceed 100, meaning that some sources saturate colors more than anequal-energy source saturates color.

Typical blackbody-like light sources and typical daylight-like lightsources have different gamut areas. Low correlated color temperaturesources (e.g., incandescent emitters) have a GAI of approximately 50%(i.e., about half the gamut area of the EES source). Sources with highercorrelated color temperature values have a larger GAL For example, avery bluish light with a correlated color temperature of 10000K may havea GAI of 140%.

Another way of characterizing how saturated an illuminant makes objectsappear is relative gamut area, or “Qg”, which is also referred to as the“Color Quality Scale Qg,” which is the area formed by (a*, b*)coordinates of the 15 test-color samples R1-R15 normalized by the gamutarea of a reference illuminant at the same correlated color temperatureand multiplied by 100. In a manner similar to GAI, Qg values can exceed100; however, Qg values are scaled for consistency relative tocorrelated color temperature. Because of chromatic adaptation, andbecause correlated color temperature is selected to set the overallcolor tone of an environment as part of the lighting design process,variable-reference measures such as Qg may be especially relevant toapplied lighting design. If the relative gamut is greater than that ofthe reference, and illuminance is lower than that provided by daylight,then an increase in preference and discrimination might be expectedrelative to the reference at that same correlated color temperature.Conversely, if the relative gamut is smaller than that of the reference,then a decrease in preference and discrimination might be expectedrelative to the reference at the same correlated color temperature.

High Qg values are generally associated with more vivid colors. It isbelieved that, in at least certain contexts, some consumers may preferlight sources with significantly enhanced vividness. It may, however, bechallenging to provide enhanced vividness in combination with highluminous efficacy, and further in combination with reasonably high colorrendering index values.

As noted above, semiconductor light emitting devices according toembodiments of the present invention may emit white light at highluminous flux values that may also have high CRI values, high CRI R9values, and enhanced vividness.

For example, according to some embodiments, semiconductor light emittingdevices are provided that include one or more LEDs that emits light in,for example, the blue color range and a recipient luminophoric mediumthat is configured to receive and down-convert at least some of thelight emitted by these LEDs. The recipient luminophoric medium includesat least a first luminescent material that down-converts a first portionof the radiation emitted by the LEDs to radiation having a first peakwavelength that is in the green or yellow color ranges; a secondluminescent material that down-converts a second portion of theradiation emitted by the LEDs to radiation having a second peakwavelength that is in the red color range, the second luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers; and a third luminescent material that down-converts a thirdportion of the radiation emitted by the LEDs to radiation having a thirdpeak wavelength that is in the red color range. The third luminescentmaterial may be narrowband luminescent material. The third peakwavelength is higher than the second peak wavelength, and the thirdluminescent material has a full-width half maximum bandwidth of lessthan 60 nanometers. In some embodiments, the third luminescent materialmay have multiple emission peaks including an emission peak that has afull-width half maximum bandwidth of less than 25 nm. Moreover, thesecond peak wavelength is within twenty (20) nanometers of the thirdpeak wavelength.

The first luminescent material may be a YAG:Ce phosphor, the secondluminescent material may be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, andthe third luminescent material may be an A₂MF₆:Mn⁴⁺ phosphor where A isan Alkali metal and M is an element with a 4+ valence. In someembodiments, the third luminescent material may be a K₂SiF₆:Mn⁴⁺phosphor having a peak wavelength between 630 and 640 nm, and the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a peak wavelength betweenabout 610 and 630 nm. The (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may havea strontium concentration of at least 0.80 in some embodiments.

The emission spectrum of the semiconductor light emitting device mayhave a first peak that is attributable to the third luminescent materialthat is at least 50% greater than any point in the emission spectrum inthe yellow or green color ranges (i.e., the luminous flux at thewavelength at which the first peak that is attributable to the thirdluminescent material is centered may be at least 50% higher than theluminous flux of the semiconductor light emitting device at any otherwavelength within the green or yellow color ranges). The thirdluminescent material may emit light having multiple distinct peaks inthe red color range, where a first of the multiple distinct peaks is ata wavelength that is less than a peak wavelength of a spectral output ofthe second luminescent material in response to the second portion of theradiation emitted by the LEDs, and a second of the multiple distinctpeaks is at a wavelength that is greater than the peak wavelength of thespectral output of the second luminescent material in response to thesecond portion of the radiation emitted by the LEDs. In someembodiments, the peak wavelength of the second luminescent material maybe between the two highest of the multiple distinct peaks of the thirdluminescent material.

A weight of the third luminescent material that is included in therecipient luminophoric medium may be at least one third the total weightof all three of the first and second and third luminescent materialsthat are included in the recipient luminophoric medium. The light outputby the semiconductor light emitting device may have a correlated colortemperature of less than 2800° K, a CRI value of at least 80, a CRI R9value of at least 30, and a Qg value of at least 100.

As another example, according to further embodiments, semiconductorlight emitting devices are provided that include one or more LEDs thatemit light in the blue color range and a recipient luminophoric mediumthat is configured to receive and down-convert at least some of thelight emitted by the blue LEDs. The recipient luminophoric mediumincludes at least a first luminescent material that down-converts afirst portion of the radiation emitted by the LEDs to radiation having afirst peak wavelength that is in the green or yellow color ranges; asecond luminescent material that down-converts a second portion of theradiation emitted by the LEDs to radiation having a second peakwavelength that is in the red color range, the second luminescentmaterial having a full-width half maximum bandwidth of at least 70nanometers; and a third narrowband luminescent material thatdown-converts a third portion of the radiation emitted by the LEDs toradiation having a plurality of distinct peaks in the red color range.The second peak wavelength may be within one of the two distinct peaksin the red color range generated by the third narrowband luminescentmaterial that have the highest spectral emission.

The first luminescent material may be a YAG:Ce phosphor, the secondluminescent material may be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, andthe third luminescent material may be a K₂SiF₆:Mn⁴⁺ phosphor. The secondluminescent material may be a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphorhaving a peak wavelength within one of the two highest spectral peaks ofthe K₂SiF₆:Mn⁴⁺ phosphor (i.e., a peak wavelength between either 612 and623 nm or between 630 and 640 nm). The emission spectrum of thesemiconductor light emitting device may have a first peak that isattributable to the third luminescent material that is at least 50%greater than any point in the emission spectrum in the yellow or greencolor ranges.

An example semiconductor device 750 that may have either of the aboveconfigurations is illustrated in FIG. 16A. As shown in FIG. 16A, therecipient luminophoric medium may, for example, be sprayed onto the LEDand also onto the reflector cup in a plurality of separate layers. Inthe depicted embodiment, the broadband red phosphor is the layer that isclosest to the LED. A performance improvement may be obtained by havingthe broadband red phosphor closer to the LED than is the YAG:Cephosphor. It will be appreciated, however, that the phosphor layers maybe deposited in other orders (e.g., the narrowband red phosphor could beclosest to the LED). Additionally, while the first through thirdluminescent materials are illustrated as being in separate layers inFIG. 16A, it will be appreciated that in other embodiments the firstthrough third luminescent materials may be contained in fewer layers(e.g., a single layer) or more than three layers, and that the recipientluminophoric medium may or may not extend onto sidewalls of the LEDand/or onto the reflector cup. The recipient luminophoric medium may, insome embodiments be conformally coated on the LED and the reflector cup.While a reflector cup is used as the mounting substrate in theembodiment of FIG. 16A, it will be appreciated that in other embodimentsa submount, leadframe or other mounting surface may be used in place ofthe depicted reflector cup.

FIG. 16B illustrates another example implementation of the abovedescribed semiconductor light emitting device in which a blue LED 760 ismounted on a mounting substrate 770 and surrounded by a reflector cup780, and the recipient luminophoric medium 790 is deposited on the LEDwithin the reflector cup. The recipient luminophoric medium 790 mayinclude all three luminescent materials mixed together. In still otherembodiments, the recipient luminophoric medium may be coated onto thechip prior to packaging.

FIGS. 17A-17D illustrate the emission spectrum for a semiconductor lightemitting device according to embodiments of the present invention (FIG.17A) as compared to various other light emitting devices (FIGS.17B-17D). Color rendering and color quality performance are alsoprovided for each light source. FIG. 17A corresponds to theabove-described semiconductor light emitting device that includes a blueLED, a YAG:Ce phosphor having a peak wavelength between 540 and 570 nm,a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having a peak wavelength between610 and 630 nm, and a K₂SiF₆:Mn⁴⁺ phosphor having a peak wavelengthbetween 630 and 640 nm. The recipient luminophoric medium includes about32% YAG:Ce phosphor, about 1% (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor andabout 67% K₂SiF₆:Mn⁴⁺ phosphor by weight. As shown in FIG. 17A, theemission spectra for this device has a small peak corresponding to theemission wavelength of the blue LED, a large, broad peak centered atabout 585 nm that trails off more quickly at higher wavelengths, and aseries of small narrow peaks extending from the large, broad peak in thered color range.

As is also shown in FIG. 17A, the light emitted by the device has acorrelated color temperature of 2728 K, a CRI value of 82, a CRI R9value of 34 and a Qg value of 101. While the CRI value may be somewhatlower than CRI values that are generally associated with very highquality white light, the high Qg value and the significant CRI R9 valueindicate that the light source emits light that will be perceived asbeing very high quality for certain applications, such as applicationswhere accurate rendering of red colored objects is important.

FIG. 17B illustrates the emission spectra for a conventionalsemiconductor light emitting device that includes a blue LED and arecipient luminophoric medium that includes a green or yellow phosphorand a broadband red phosphor. As can be seen, the emission spectra forthis device has a conventional shape, and includes significantcontributions falling at wavelengths above 650 nm, where the response ofthe human eye to such colored light is quite poor. This suggests thatthe light emitting device will not achieve good luminous fluxperformance as compared to the light emitting device associated with theemission spectra of FIG. 17A. A comparison of the performance dataincluded in FIGS. 17A and 17B also shows that the light emitting deviceassociated with the emission spectra of FIG. 17B generates lower qualitylight, having a slightly lower CRI value, a lower Qg value (95 versus101 for the device of FIG. 17A) and a significantly lower CRI R9 value(15 versus 34 for the device of FIG. 17A).

FIG. 17C illustrates the emission spectra for a conventionalsemiconductor light emitting device that includes at least oneblue-shifted yellow LED (i.e., a blue LED with an associated recipientluminophoric medium that includes a phosphor that emits yellow light)combined with at least one red light emitting LED, which is sometimesreferred to as a “True White” light emitting device. As can be seen, theemission spectra for this device has the conventional shape for ablue-shifted yellow LED, along with a high peak in the red color rangecorresponding to the red LED. A comparison of the performance dataincluded in FIGS. 17A and 17C also shows that the True White lightemitting device generates high quality light having a CRI of 92, a veryhigh CRI R9 of 96 and a Qg value of 108, although the True White lightemitting device emits light at a higher correlated color temperature(3026 K) where it may be easier to exhibit improved color quality.

However, the semiconductor light emitting devices according toembodiments of the present invention may provide a number of advantagesas compared to the True White light emitting device of FIG. 17C in termsof simplicity and cost. As noted above, the True White light emittingdevice uses both phosphor converted blue LEDs along with separate redLEDs, and hence the True White light emitting devices may require anoptical mixing element and/or a mixing chamber to allow the light fromthe separate sources to mix to provide the white light output. The useof such mixing elements and/or chambers increases both the complexityand cost of the device. Moreover, in some applications, such as certainapplications for the replacement of fluorescent lighting, the physicaldimensions may make it difficult to perform the mixing required inapproaches using multiple different color solid state lighting sources.Moreover, red LEDs are fabricated using different semiconductormaterials than blue LEDs, and hence exhibit different thermal behavior.As one example, red LEDs tend to degrade in luminous efficiency morestrongly than blue LEDs with increasing operating temperature. Thus, inorder to generate light having consistent color characteristics as afunction of temperature, circuitry may be required that increases thecurrent supplied to the red LEDs with increasing temperature in order tomaintain a consistent color point. This again increases the cost andcomplexity of the True White light emitting devices, and the reducedluminous efficiency of the red LEDs at elevated temperatures may degradethe luminous flux of the device. In contrast, the semiconductor lightemitting devices according to embodiments of the present invention maynot include mixing elements, mixing chambers, separate red LEDs and/orcircuitry that increases the current supplied to the red LEDs withincreasing temperature.

FIG. 17D illustrates the emission spectra for a semiconductor lightemitting device that includes a blue LED and a recipient luminophoricmedium that includes a YAG:Ce phosphor and a K₂SiF₆:Mn⁴⁺ phosphor havinga peak wavelength between 630 and 640 nm. The recipient luminophoricmedium includes about 17% YAG:Ce phosphor and 83% K₂SiF₆:Mn⁴⁺ phosphorby weight. As shown in FIG. 17D, the emission spectra for this devicehas a small peak corresponding to the emission wavelength of the blueLED, a large, broad peak centered at about 550 nm, and a series ofsmall, high peaks extending from the large, broad peak in the red colorrange. A comparison of the performance data included in FIGS. 17A and17D shows that the light emitting device associated with the emissionspectra of FIG. 17D also generates high quality light having a CRI valueof 90, CRI R9 value of 94, and a Qg value of 109. However, as theK₂SiF₆:Mn⁴⁺ phosphor is more expensive than conventional red phosphors,and less potent, the light emitting device associated with the emissionspectra of FIG. 17D may be very expensive to implement, and may be moredifficult to make due to the sheer quantity of phosphor required.

By comparing FIGS. 17A and 17D, it can be seen that somewhat similarcolor rendering performance is provided by the two devices, with thedevice of FIG. 17D providing enhanced performance, but doing so atincreased cost. The difference between these two devices is thepercentage of the phosphors included in the luminophoric medium, withthe device of FIG. 17A including about 65% of K₂SiF₆:Mn⁴⁺ phosphor byweight, about 33% of YAG:Ce phosphor by weight and about 1-2%(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor by weight, while the device of FIG.17D includes, about 83% of K₂SiF₆:Mn⁴⁺ phosphor by weight, about 17% ofYAG:Ce phosphor by weight and no (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.It will be appreciated, however, that different ratios may be used. Forexample, in other embodiments, the recipient luminophoric medium mayinclude between about 30% and 90% K₂SiF₆:Mn⁴⁺ phosphor by weight,between about 0.5% and 10% of (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor byweight, and between about 15% and 60% YAG:Ce by weight. In otherembodiments, the recipient luminophoric medium may include between about50% and 75% K₂SiF₆:Mn⁴⁺ phosphor by weight, between about 1% and 10% of(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor by weight, and between about 15%and 49% YAG:Ce by weight.

The ratio, by weight of the K₂SiF₆:Mn⁴⁺ phosphor to the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may be at least 40:1 in someembodiments. In other embodiments this ratio may be at least 30:1. Instill other embodiments this ratio may be at least 25:1. In still otherembodiments this ratio may be at least 20:1. In yet further otherembodiments this ratio may be at least 15:1.

As shown above, the semiconductor light emitting devices according toembodiments of the present invention may provide both good CRI valuesand high to very high CRI R9 values, while also providing very highoverall color quality, and may do so while also providing high luminousflux values, which is a commercial necessity in many if not mostapplications. Meeting all of these criteria in a light emitting devicethat comprises a single LED chip with an associated recipientluminophoric medium may be a challenge, however, using conventionaltechniques.

FIG. 18 is an emission spectra plot that helps illustrate thischallenge. In particular, FIG. 18 plots the emission spectra for thesemiconductor light emitting devices associated with FIGS. 17B and 17Dabove, along with the eye response curve that illustrates thesensitivity of the human eye to light of various wavelengths and the CRIR9 reflectivity spectrum. As can be seen in FIG. 18, the peaks in theeye response curve and the CRI R9 reflectivity spectrum have very littleoverlap, and it is only in a very tight wavelength range of about 615 to635 nm that light provides significant contribution in terms of bothluminous flux and CRI R9. Thus, to obtain a high CRI R9 value while alsomaintaining high luminous efficiency it may be necessary to concentratethe bulk of the red light emission spectrum in this narrow wavelengthrange.

As can be seen in FIG. 18, the emission spectrum for the conventionalsemiconductor light emitting device of FIG. 17B does not accomplishthis, as there is a long emission tail in the red color range thatextends beyond 635 nm where the eye has almost no sensitivity to thelight, and hence the luminous efficiency of the device is reduced.Additionally, the wide emission bandwidth from the red phosphor used inthis device does a poor job of concentrating energy in the wavelengthrange necessary to achieve high CRI R9 values, which is why this devicewill have a CRI R9 value of only about 15. Such a device will generallynot do a good job of accurately rendering the color of red objects.

In contrast, the semiconductor light emitting device associated withFIG. 17D, which has a recipient luminophoric medium that includes aYAG:Ce phosphor (about 17% by weight) and a K₂SiF₆:Mn⁴⁺ phosphor (about83% by weight) concentrates almost all of the red emission in the615-635 nm wavelength range where there is still reasonable eyesensitivity and good CRI R9 response. This semiconductor light emittingdevice may provide a CRI R9 value of about 94 while still maintaininghigh luminous efficiency.

As discussed above, the semiconductor light emitting devices accordingto embodiments of the present invention may include a variety of ratiosof a broadband red phosphor (e.g., a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor) to a narrowband red phosphor (e.g., a K₂SiF₆:Mn⁴⁺ phosphor).FIG. 19 compares the emission spectrum of two different semiconductorlight emitting devices having two different ratios, namely a firstdevice in which the narrowband red (“NBR”) phosphor comprises about 40%of the total amount of phosphor by weight (which total includes thegreen/yellow phosphor), and which also includes a broadband red “(BBR”)phosphor, and a second device that includes only the narrowband redphosphor (representing about 83% of the total amount of phosphor byweight). As can be seen in FIG. 19, the individual peaks associated withthe narrowband red phosphor are only about half as high for the firstdevice as compared to the second device, but the first device doesexhibit increased emission in the 550-600 nm wavelength range, as wellas increased emission at wavelengths above 650 nm. For comparativepurposes, the emission spectra for an incandescent light bulb and for aconventional phosphor converted blue LED (e.g., the LED associated withFIG. 17B above) are plotted in FIG. 19 as well.

It will be appreciated that the semiconductor light emitting devices ofFIG. 16A-16B can be used in a wide variety of packages to providecomponents and/or in bulbs or fixtures to provide lighting devices. Forexample, FIG. 20A is a schematic a schematic cross-sectional view of alight bulb 700 that includes semiconductor light emitting devices 710according to embodiments of the present invention. FIG. 20B is aschematic plan view of a mounting substrate 720 that is included in thelight bulb 700 of FIG. 20A. The mounting substrate 720 includes aplurality of the semiconductor light emitting devices according toembodiments of the present invention mounted thereon.

It will also be appreciated that additional phosphors may be included inthe recipient luminophoric medium of the LEDs shown in FIGS. 16A, 16Band 20. For example, a portion of the YAG:Ce phosphor may be replacedwith a LuAG:Ce phosphor. This will typically result in a decrease in theluminous flux performance of the device and an increase in the CRI valueof the device. As another example, some of the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may be replaced with a higher peakwavelength (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor as is done in otherembodiments of the present invention that are discussed above.

In some embodiments, the blue LEDs that are used may be a relativelyshort wavelength blue LEDs having a wavelength of 455 nm or less. Theuse of shorter wavelength blue LEDs may help achieve higher Qg values.However, at very low blue wavelengths, reliability may decrease as willthe efficiency of the emission from the LED in exciting the YAG:Cephosphor. Accordingly, in some embodiments, blue LEDs having peakwavelengths in the range of about 445 nm to about 455 nm may bepreferred.

The above-described semiconductor light emitting devices according toembodiments of the present invention may exhibit high luminous flux,high quality color rendering, a good ability to accurately reproduce redcolors, and overall high color quality and vividness. Thesesemiconductor light emitting devices may be incorporated intocomponents, bulbs and/or fixtures that do not include any red lightemitting LEDs.

The above-described semiconductor light emitting devices havingrecipient luminophoric mediums that include a yellow phosphor, abroad-spectrum red phosphor and a narrow-spectrum red phosphor may bepreferred over the semiconductor light emitting devices having twobroad-spectrum red phosphors, a narrow-spectrum red phosphor and a greenphosphor in some applications. In these devices, the peak wavelength ofthe broad-spectrum red phosphor and the peak-wavelength of thenarrow-spectrum red phosphor may be very close together, which isnon-intuitive as it tends to bunch the spectral combination of the twored phosphors in a narrow range as opposed to filling in gaps betweenthe peak wavelengths for various phosphors. The omission of the secondbroad-spectrum red phosphor may generally (but not necessarily always)act to reduce the CRI of the device, but tends to increase the luminousefficiency of the device as the broad-spectrum red phosphor that isomitted is the one with the higher peak wavelength.

In some embodiments, the narrow-spectrum red phosphor may comprise aK₂SiF₆:Mn⁴⁺ phosphor that has an emission spectrum with multipledistinct peaks, all of which are in the red color range. The highest ofthese peaks is at about 635 nm, and the second highest of these peaks isat about 615 nm. As discussed above, in some embodiments, thebroad-spectrum red phosphor that is included in the recipientluminophoric medium may have a peak wavelength that is in between thesetwo peaks (e.g., a peak wavelength between 615 and 635 nm). In otherembodiments, the broad-spectrum red phosphor that is included in therecipient luminophoric medium may have a peak wavelength that is withinone of these two peaks (i.e., a peak wavelength between about 612 and623 or between about 630 and 640 nm). These are non-intuitiveapproaches, as they act to group the two red phosphors in the sameportion of the emission spectrum as opposed to spreading the emissionpeaks of the phosphors out to fill in gaps in the emission spectrum forthe device.

A tradeoff may exist based on the amount of red phosphors versus theamounts of yellow and/or green phosphors included in the recipientluminophoric mediums of semiconductor light emitting devices accordingto certain embodiments of the present invention. In particular,increasing the relative amount of red phosphor may generally improve theR9 and Qg performance of the device, and may also provide someimprovement to the overall CRI of the device. Thus, increasing therelative amount of red phosphor (up to a certain point) may generallycorrespond to increased color quality. However, this typically comes atthe cost of a decrease in the luminous flux of the device. For example,TABLE 2 compares the luminous flux and color quality performance of fourexample semiconductor light emitting devices according to embodiments ofthe present invention. The above-described tradeoff between colorquality and luminous flux may clearly be seen in the data presented inTABLE 2.

TABLE 2 NBR % of NBR % of Relative Red Total CCT Luminous PhosphorPhosphor Phosphor Combination (K) Flux CRI R9 Qg (Weight) (Weight) YAG +BBR + NBR 2700 107 82 5 91 0.76 0.33 YAG + LuAG + BBR + NBR 2700 105 8330 100 0.94 0.63 YAG + BBR + NBR 2700 106 85 50 105 0.98 0.74 YAG + NBR2700 102 90 92 111 1.00 0.83 Conventional Device 1 2700 100 81 5 95 0 0Conventional Device 2 2700 83 91 55 101 0 0

In TABLE 2, “YAG” refers to a YAG:Ce phosphor, “LuAG” refers to aLuAG:Ce phosphor, “BBR” refers to a broadband red phosphor, which inthis case was a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and “NBR” refersto a narrowband red phosphor, which in this case was a K₂SiF₆:Mn⁴⁺phosphor. “CCT” stands for correlated color temperature, and the lasttwo columns of TABLE 2 show the percentage, by weight, that thenarrowband red phosphor made up of the total amount of red phosphor andthe percentage, by weight, that the narrowband red phosphor made up ofthe total amount of phosphor, respectively. The general trend towardincreased color quality at the cost of a reduction in luminous flux thatis discussed above can be seen in the data in TABLE 2.

For comparative purposes, performance data is also provided in TABLE 2for two conventional state of the art semiconductor light emittingdevices labeled “Conventional Device 1” and “Conventional Device 2.” Asis readily apparent, these devices generally exhibit worse performancein terms of both color quality and luminous flux as compared to thesemiconductor light emitting devices according to embodiments of thepresent invention. FIGS. 21A and 21B are graphs of CRI and Qg versusluminous flux, respectively that illustrate the data presented in TABLE2 above. These graphs clearly show the improved performance provided bythe semiconductor light emitting devices according to embodiments of thepresent invention as well as the tradeoff between luminous flux andcolor quality performance.

In some embodiments, the amounts of the YAG:Ce, LuAG:Ce, broadband redand narrowband red phosphors may be varied to achieve different levelsof color quality, luminous flux and cost performance. In a first suchembodiment, a LuAG:Ce phosphor may comprise about 60-70% of the totalamount of phosphor by weight, a narrowband red phosphor may compriseabout 20-30% of the total amount of phosphor by weight, and a broadbandred phosphor may comprise about 10-20% of the total amount of phosphorby weight. In such embodiments, the LuAG:Ce phosphor may have a peakwavelength between about 535 and 550 nm, the narrowband red phosphor mayhave a peak wavelength between about 625 and 635 nm, and the broadbandred phosphor may have a peak wavelength between 610 and 630 nm or, morepreferably, between 612 and 625 nm.

In a second such embodiment, a LuAG:Ce phosphor may comprise about 5-15%of the total amount of phosphor by weight, a YAG:Ce phosphor maycomprise about 15-30% of total amount of phosphor by weight, anarrowband red phosphor may comprise about 60-70% of the total amount ofphosphor by weight, and a broadband red phosphor may comprise about2-10% of the total amount of phosphor by weight. In such embodiments,the LuAG:Ce phosphor may have a peak wavelength between about 535 and550 nm, the YAG:Ce phosphor may have a peak wavelength between about 550and 560 nm, the narrowband red phosphor may have a peak wavelengthbetween about 625 and 635 nm, and the broadband red phosphor may have apeak wavelength between 610 and 630 nm or, more preferably, between 612and 625 nm.

In a third such embodiment, a YAG:Ce phosphor may comprise about 20-30%of the total amount of phosphor by weight, a narrowband red phosphor maycomprise about 70-80% of the total amount of phosphor by weight, and abroadband red phosphor may comprise about 2-8% of the total amount ofphosphor by weight. In such embodiments, the YAG:Ce phosphor may have apeak wavelength between about 550 and 560 nm, the narrowband redphosphor may have a peak wavelength between about 625 and 635 nm, andthe broadband red phosphor may have a peak wavelength between 610 and630 nm or, more preferably, between 612 and 625 nm.

The second and third embodiments discussed above could also be modifiedto have less of the broadband red phosphor by weight. For example, thelower limit on the percentage of the broadband red phosphor by weightmay be reduced from 2% to 1% or even to 0.5% in further embodiments.

In each of the above embodiments, the recipient luminophoric medium maybe used with a blue LED having a peak wavelength of, for example,between 450 and 455 nm.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

For example, a wide variety of semiconductor light emitting devices aredescribed above that include a blue LED having an associated recipientluminophoric medium that includes at least a broadband green and/oryellow light emitting luminescent material (e.g., a YAG:Ce or LuAG:Cephosphor), at least one broadband red light emitting luminescentmaterial (e.g., a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor) and a narrowbandred light emitting luminescent material (e.g., a K₂SiF₆:Mn⁴⁺ phosphor).It will be appreciated that the recipient luminophoric mediums for thesesemiconductor light emitting devices may be deposited on the blue LEDsusing any of the techniques described herein, and that the recipientluminophoric mediums may have any of the different configurationsdiscussed herein in term of the portion of the LED that they cover andthe particular layer structure (e.g., a single layer recipientluminophoric medium or a multi-layer recipient luminophoric medium).Likewise, these semiconductor light emitting devices may compriseindividual LEDs, packaged components including one or more of the LEDs,and/or light fixtures or light bulbs. For example, any of thesemiconductor light emitting devices disclosed herein could be used inas the light emitting devices in the packaged components, fixtures andlight bulbs of FIGS. 9, 10 and 20.

The present invention has been described above with reference to theaccompanying drawings, in which certain embodiments of the invention areshown. However, this invention should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the thickness of layers and regions are exaggerated forclarity. Like numbers refer to like elements throughout. As used hereinthe term “and/or” includes any and all combinations of one or more ofthe associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that, when used in thisspecification, the terms “comprises” and/or “including” and derivativesthereof, specify the presence of stated features, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, operations, elements, components, and/or groupsthereof.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions and/orlayers, these elements, components, regions and/or layers should not belimited by these terms. These terms are only used to distinguish oneelement, component, region or layer from another element, component,region or layer. Thus, a first element, component, region or layerdiscussed below could be termed a second element, component, region orlayer without departing from the teachings of the present invention.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the figures. Forexample, if the device in the figures is turned over, elements describedas being on the “lower” side of other elements would then be oriented on“upper” sides of the other elements. The exemplary term “lower”, cantherefore, encompasses both an orientation of “lower” and “upper,”depending on the particular orientation of the figure.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

What is claimed is:
 1. A semiconductor light emitting device that emitslight in at least a blue color range, a green color range, a yellowcolor range and a red color range, comprising: a light emitting diode(“LED”); and a recipient luminophoric medium that is configured todown-convert at least some of the light emitted by the LED, therecipient luminophoric medium including at least: a first luminescentmaterial that down-converts a first portion of the radiation emitted bythe LED to radiation having a first peak wavelength that is in the greencolor range or the yellow color range; a second broad-spectrumluminescent material that down-converts a second portion of theradiation emitted by the LED to radiation having a second peakwavelength that is in the red color range; a third K₂SiF₆:Mn⁴⁺ phosphorthat down-converts a third portion of the radiation emitted by the LEDto radiation having a third peak wavelength that is in the red colorrange; and a fourth broad-spectrum luminescent material thatdown-converts a fourth portion of the radiation emitted by the LED toradiation having a fourth peak wavelength that is different than thefirst, second and third peak wavelengths, wherein the second peakwavelength is within twenty (20) nanometers of the third peak wavelengthand the third peak wavelength is different than the second peakwavelength.
 2. The semiconductor light emitting device of claim 1,wherein a peak of the spectral output of the semiconductor lightemitting device that is attributable to the third luminescent materialis at least 1.5 times the spectral output of the semiconductor lightemitting device at the second peak wavelength.
 3. The semiconductorlight emitting device of claim 1, wherein the third peak wavelength isgreater than the second peak wavelength.
 4. The semiconductor lightemitting device of claim 1, wherein the K₂SiF₆:Mn⁴⁺ phosphor hasmultiple distinct peaks, and wherein the two of the multiple distinctpeaks having the highest spectral output have peak wavelengths that areon either side of the second peak wavelength.
 5. The semiconductor lightemitting device of claim 1, wherein the second peak wavelength is within10 nm of the third peak wavelength.
 6. The semiconductor light emittingdevice of claim 1, wherein the third peak wavelength is within 15nanometers of the combined spectral output of the second and fourthbroad-spectrum luminescent materials.
 7. The semiconductor lightemitting device of claim 1, wherein the third peak wavelength is within10 nanometers of the combined spectral output of the second and fourthbroad-spectrum luminescent materials.
 8. The semiconductor lightemitting device of claim 1, wherein the second broad-spectrumluminescent material is a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having apeak wavelength between 610-620 nanometers and the fourth broad-spectrumluminescent material is a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having apeak wavelength between 621-630 nanometers.
 9. The semiconductor lightemitting device of claim 1, wherein the fourth peak wavelength is in thered color range.
 10. A semiconductor light emitting device that emitslight in at least a blue color range, a green color range, a yellowcolor range and a red color range, comprising: a light emitting diode(“LED”); and a recipient luminophoric medium that is configured todown-convert at least some of the light emitted by the LED, therecipient luminophoric medium including at least: a first luminescentmaterial that down-converts a first portion of the radiation emitted bythe LED to radiation having a first peak wavelength that is in the greenor yellow color ranges; a second luminescent material that down-convertsa second portion of the radiation emitted by the LED to radiation havinga second peak wavelength that is in the red color range, the secondluminescent material having a full-width half maximum bandwidth of atleast 70 nanometers; a third luminescent material that down-converts athird portion of the radiation emitted by the LED to radiation having athird peak wavelength that is in the red color range and that is higherthan the second peak wavelength, the third luminescent material havingan emission peak that has a full-width half maximum bandwidth of lessthan 25 nanometers, wherein the second peak wavelength is within twenty(20) nanometers of the third peak wavelength, wherein the thirdluminescent material emits light having multiple distinct peaks in thered color range, and wherein a first of the multiple distinct peaks isat a wavelength that is less than the second peak wavelength, and asecond of the multiple distinct peaks is at a wavelength that is greaterthan the second peak wavelength, and wherein the first and second of themultiple distinct peaks are the highest two of the multiple of thedistinct peaks.
 11. The semiconductor light emitting device of claim 10,wherein the third luminescent material comprises a K₂SiF₆:Mn⁴⁺ phosphorhaving a peak wavelength between 630 and 640 nm, and wherein the secondluminescent material is a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor having apeak wavelength between 610 and 630 nm.
 12. The semiconductor lightemitting device of claim 11, wherein an emission spectrum of thesemiconductor light emitting device includes a first peak that isattributable to the third luminescent material that is at least 50%greater than any point in the emission spectrum of the semiconductorlight emitting device in the yellow or green color ranges.
 13. Thesemiconductor light emitting device of claim 10, wherein the firstluminescent material is a YAG:Ce phosphor, the second luminescentmaterial is a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and the thirdluminescent material is an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkalimetal and M is an element with a 4+ valence.
 14. The semiconductor lightemitting device of claim 10, wherein a ratio of the third luminescentmaterial to the combination of the first and second luminescentmaterials by weight is at least 2:3, and wherein a ratio of an amount ofthe third luminescent material by weight to an amount of the secondluminescent material by weight is at least 25:1.
 15. The semiconductorlight emitting device of claim 10, wherein the light output by thesemiconductor light emitting device has a correlated color temperatureof between 2700 K and 2850 K, a CRI value of between 80 and 92, a CRI R9value of between 30 and 70, and a Qg value of between 90 and
 110. 16.The semiconductor light emitting device of claim 15, wherein thesemiconductor device is part of a bulb or fixture that does not includeany light emitting diodes that emit red light.
 17. The semiconductorlight emitting device of claim 10, wherein the third luminescentmaterial emits light having multiple distinct peaks in the red colorrange, and wherein a peak wavelength of a spectral output of the secondluminescent material in response to the second portion of the radiationemitted by the LED is at a wavelength that is within the highest orsecond highest of the multiple distinct peaks.
 18. A semiconductor lightemitting device, comprising: a light emitting diode (“LED”) that emitslight having a peak wavelength in a blue color range; and a recipientluminophoric medium that is configured to down-convert at least some ofthe light emitted by the LED, the recipient luminophoric mediumincluding at least: a YAG:Ce phosphor; a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor that down-converts a second portion of the radiation emitted bythe LED to radiation having a second peak wavelength that is between 610and 635 nm; an A₂MF₆:Mn⁴⁺ phosphor where A is an Alkali metal and M isan element with a 4+ valence that down-converts a third portion of theradiation emitted by the LED to radiation having a third peak wavelengththat is between 625 and 640 nm, the third luminescent material having afull-width half maximum bandwidth of between 25 and 55 nm, wherein thesecond peak wavelength is within twenty (20) nanometers of the thirdpeak wavelength, wherein the semiconductor light emitting device emitslight having a CRI value of between 80 and 92, a CRI R9 value of between30 and 70, a correlated color temperature of between 2700 K and 2850 K,and a Qg value of between 90 and 110, wherein an emission spectrum ofthe semiconductor light emitting device includes a first peak that isattributable to the A₂MF₆:Mn⁴⁺ phosphor that has a magnitude that is atleast twice the magnitude of any point in emission spectrum in theyellow or green color ranges, and wherein the A₂MF₆:Mn⁴⁺ phosphor is atleast 70% of the total weight of the combination of the YAG:Ce,A₂MF₆:Mn⁴⁺ and (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors.
 19. Thesemiconductor device of claim 18, wherein the A₂MF₆:Mn⁴⁺ phosphor emitslight having multiple distinct peaks in the red color range, and whereina highest of the multiple distinct peaks is at a wavelength that isgreater than a peak wavelength of a spectral output of the and(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor, and a second highest of themultiple distinct peaks is at a wavelength that is less than the peakwavelength of the spectral output of the (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor.
 20. The semiconductor device of claim 18, wherein theA₂MF₆:Mn⁴⁺ phosphor emits light having multiple distinct peaks in thered color range, and wherein a peak wavelength of a spectral output ofthe (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor in response to the secondportion of the radiation emitted by the LED is at a wavelength that iswithin the highest or second highest of the multiple distinct peaks. 21.The semiconductor device of claim 18, wherein a ratio of an amount ofthe A₂MF₆:Mn⁴⁺ phosphor by weight to an amount of the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor by weight is at least 25:1.